Materials for the Study of the Pelecypod Fauna of the Kolchugino Series of the Kuznetsk Coal Basin

Mining engineer L. L. Khalfin.

From the Author

The work published below was carried out by me in 1935 on assignment from the Kuzbassugol’ Research Institute; its publication was greatly delayed, and during the three years that have passed since the completion of this work, a number of materials have appeared that directly concern the questions touched upon in my work. First of all, the works of D. M. Fedotov (42; 43) must be mentioned, in which the pelecypod fauna from the coal-bearing deposits of Kuzbass is for the first time objectively and thoroughly described. Having become acquainted with the materials of D. M. Fedotov, I did not consider the publication of my own work superfluous, although the material of the latter is partly covered by the works of this author and the final conclusions about the Permian age of the fauna in D. M. Fedotov and in myself coincide. The reasons that prompted me to publish this work are as follows.

1. Among the pelecypods described by D. M. Fedotov (as also by me), there is not a single form identical with any previously described species from deposits developed outside the Kuznetsk Basin. At the same time, in our fauna there are forms that reveal a significant similarity both to Carboniferous and to Permian species, and this applies not only to the lower, but also to the upper part (the Kolchugino Series) of the Paleozoic productive sequence of Kuzbass. Thus, according to the data of D. M. Fedotov, even among the pelecypods of the Kolchugino Series there are, along with four forms close to Permian species, three species very close to Carboniferous species.

In my work I try to answer the questions—why a number of forms in the Permian fauna of Kuzbass have a Carboniferous aspect and why the Permian, and not Carboniferous, elements of this fauna must have decisive significance in determining its age. Among previously described faunas there are no faunas analogous to the fauna of the coal-bearing deposits of Kuzbass; the latter has to be compared either with isotopic but differently aged (Carboniferous) faunas, or with synchronous (Permian) but heterotopic faunas. I regard this proposition, derived from an analysis of the non-marine facies of the Upper Paleozoic, as fundamental: my article (44) in Problems of Soviet Geology¹ is devoted to this question, and from this point of view I analyze the pelecypod fauna of the Kolchugino Series in the present work.

1. Another circumstance, to which I am inclined to attach substantial importance and which also serves for me as an incentive to publish this work, consists in the different understanding of the scope of a species in the works of D. M. Fedotov and in my own: if in my work, among the pelecypods of the Kolchugino Series, within the genera Anthracomya Salt., Anthraconauta Pruvost and Palaeanodonta Amal. 17 forms are described, then in D. M. Fedotov, who had very extensive collections at his disposal, only 6 forms are assigned to these genera. It is enough to examine the descrip-

...descriptions and illustrations of such species as Anthraconauta pseudophillipsii Fedotov and Anthraconauta iljinskiensis Fedotov (42, pp. 35–37), in order to be convinced that this author accepts a very broad scope for the species he describes; I, on the other hand, consciously risking reproach for establishing independent species on the basis of very small differences in shell morphology, in my work adopt a narrow scope for the forms I describe.

I am far from considering myself absolutely right on this question, and am prepared to admit that some of the species I have described have a provisional character¹), if one takes into account the extraordinary individual variability established for a number of modern mollusk species. But, unfortunately, “paleontological material, especially in such a group as the pelecypods, often provides no objective criteria for establishing boundaries between species” (40, 9), since it has been established that in many modern mollusk species, for example in Chlamis islandicus Müller, within a species there vary such characters as in paleontology often have to be used as specific distinctions, which, of course, introduces a considerable element of subjectivity into determinations” (41, 4). Thus a paleontologist engaged in the study of groups similar to pelecypods inevitably finds himself faced with considerable difficulties. Under these conditions, at the first stages in the study of any fauna, it seems to me that one should adopt the direction of work whose essence was formulated, for example, by A. P. Pavlov in the preface to his description of the Viviparidae of the Neogene and Quaternary: “In this work I have tried to make the broadest possible use of the morphological differences of the forms under study that alone are accessible to the paleontologist, and to single out under special names all paludines that can be distinguished by one character or another, provided they do not represent isolated, perhaps accidental deviations. It is not excluded that males and females of one and the same species will thereby be designated by different names, but this does not harm the comparative stratigraphy of the deposits, which is the principal task of this work. A detailed paleontological treatment of the material may reduce the number of separate forms by uniting them into larger units, but such a treatment, as has already been noted above, is not part of the task of this investigation, and for the time being analysis must precede synthesis” (46, 132).

Even if, as applied to a modern fauna, the delimitation of species and of smaller units (morph, subspecies geographica, subspecies oecologica, etc.) presents difficulties and leads to disagreements, I see no possibility whatever of doing this with respect to a fossil and as yet quite insufficiently studied fauna. If, moreover, one takes into account the considerable morphological uniformity of the pelecypods of the Carbonicola facies (which is discussed in greater detail below), then the known danger of overestimating individual variability becomes obvious, i.e., the danger of assigning to one species a number of different forms (as is the case, for example, in Hind’s well-known monograph; see below). And I consider it absolutely obligatory (especially at the first stages in the study of any new fauna) to record precisely and clearly all variations, all changes that can be established in the given fauna. Further investigations, with the accumulation of knowledge on the given fauna, will introduce the necessary corrections and will lead to the delimitation of species, varieties, and modifications. In this sense I consider it a lesser evil to establish several species that may later be united, than to “reduce” essentially different forms to one species.

Thus the “species” in the works of D. M. Fedotov and the “species” in my work are, in a number of cases, units that are difficult to compare. This has confronted me with certain difficulties already in the matter of naming species: since D. M. Fedotov’s works were published before mine, by right of priority the specific names proposed by D. M. Fedotov should be extended also to some of the species described by me. However, the different interpretation of the scope of the species adopted by D. M. Fedotov and by me makes this very difficult. Thus, within the species Anthraconauta pseudophillipsii Fedotov there are apparently forms that I refer to the species Anthraconauta obliqua

¹) This, incidentally, applies to very many fossil species of pelecypods in general.

Anthraconauta tschernyschewi and Anthraconauta tomiensis, species with whose unification I cannot agree. Since neither in the descriptions nor on the labels in the collection are the holotypes of the species established by D. M. Fedotov indicated, I refrained from the intention of replacing one of these three names with the name Anthraconauta pseudophillipsii, all the more so because among the specimens called by D. M. Fedotov by this name there apparently are forms deserving separation as independent species and absent from my collection. Therefore, while retaining my species names, in the descriptions of the latter I give comparisons with the species established by D. M. Fedotov, insofar as I can do this on the basis of examining his collection. This examination,^1 however, convinced me that a number of forms described by me are absent from D. M. Fedotov’s collection, and, conversely, in my collection I did not find some forms described by D. M. Fedotov. This once again emphasizes how incompletely our fauna has yet been studied.

1. Finally, in the interpretation of certain forms of the pelecypod fauna of the Kolchugino Suite I must make remarks based on the study of the material available to me and illuminating these forms in a different light. First of all this applies to those species which Jones assigned to the genus Posidonomya Bronn and which D. M. Fedotov assigns to the genus Abiella Rag.

I considered it necessary both in this preface and in the text published below to formulate with complete clarity those disagreements which I have with D. M. Fedotov concerning the fauna of the Kolchugino pelecypods. In doing so, I in no way intend to diminish the importance of the works of D. M. Fedotov, which play a capital role in the study of our fauna; rather, I pursue the single aim of contributing to the most comprehensive elucidation of paleontological material that is extremely difficult to study and important in scientific and practical respects.

In preparing the present work for publication, I had the opportunity to become acquainted (besides newly published works) with a number of sources that had not been at my disposal when I was processing the fauna, and also with collections described by M. E. Yanishevsky, B. I. Chernyshev, and D. M. Fedotov. The study of all these materials did not entail the need for me to rework the manuscript in any substantial way, but in a number of cases it proved necessary to make certain additions; these additions are set in petit type and enclosed in square brackets; additionally cited literary sources are marked in the bibliography with an asterisk.

As for changes in the determinations, they amounted to the following:

1. The species Anthracomya fedotovi in the manuscript of 1935 figured under the name Anthracomya ovata Tschern.; acquaintance with the Donets Basin originals of this species convinced me that in Kuzbass we have a form only in certain respects close, but by no means identical.

2. The species Anthraconauta obliqua in the manuscript of 1935 was called Anthracomya minima Hind n. var. rotundata; since the close genetic relationship of our form with Hind’s species is more than doubtful, I considered it more correct to separate it as an independent species.

^1 For a detailed study of these collections I did not have the time.

PREFACE

In the spring of the current year I received a proposal from the Tomsk Branch of the Scientific-Research Institute of Kuzbass Coal to work up the pelecypod fauna from the Kolchugino Series of the Kuznetsk coal basin.

Following with understandable interest the discussion on the stratigraphy of the productive deposits of Kuzbass, I readily accepted the proposal, as an opportunity to become more closely acquainted with the fauna of at least one of the series, all the more since this work was also to touch upon and, to some extent, illuminate one particular disputed question—namely, the question of the age of the deposits of the Kolchugino Series, a question resolved differently by paleophytologists and by paleozoologists.

The material to be worked up was to be a collection of pelecypods from the Leninsk Mine and the Ilyinsko-Erunakovsky open cut. The faunal collections were made by students of the Tomsk Industrial Institute, P. A. Stavsky and M. I. Kazantsev. The extensive collection delivered from the Ilyinsko-Erunakovsky open cut made it possible to study the given fauna in sufficient detail. Unfortunately, the Tomsk Branch of the Scientific-Research Institute of Kuzbass Coal did not obtain core material from the Leninsk Mine Administration, and at my disposal from the Leninsk Mine there proved to be only a very scanty fauna, collected chiefly from mine dumps.

Student of Tomsk State University I. V. Lebedev took part in the processing of the fauna. The drawings in the text belong to artist V. P. Mizerov.

The work was carried out at the Department of Historical Geology of the S. M. Kirov Tomsk Industrial Institute, with the unfailing assistance and consultation of the head of the department, Prof. M. K. Korovin.

November, 1935.

INTRODUCTION.

I consider it necessary, before describing and analyzing the paleontological material at my disposal, to set forth its general characteristics and to make several methodological remarks that will make it possible to take into account both the specific features of our fauna and the peculiarities of its treatment that follow from them.

The fauna of the coal-bearing deposits of the Kuznetsk coal basin is quite diverse and is represented by a large number of animal groups. From these deposits various authors have described or indicated reptiles, fishes, various crustaceans, insects, mollusks, brachiopods, worms, and crinoids. However, not all these groups are equally widespread in the productive series; above all, the typical marine fauna (brachiopods and the corresponding mollusks) is confined only to the lowest horizons of these deposits, although elements of the marine fauna (Lepadidae, Annelidae, Crinoidea, and some Pelecypoda) are apparently still fairly common in the Balakhon suite. The groups that are predominantly distributed and, consequently, are of practical interest for purposes of stratigraphy are only Ostracoda and Pelecypoda. In particular, in the Kolchugino suite, to which the present work is devoted, these two groups are predominant. Leaving aside the ostracods, which have as yet been studied in Kuzbass quite insufficiently, and turning to the lamellibranch mollusks, it should first be noted that everywhere, at all localities and in all areas where the Kolchugino suite is developed, the deposits of the latter contain a fauna of these mollusks. And the small literature that exists on the pelecypods from the coal-bearing deposits of Kuzbass concerns, in the majority of cases, precisely the pelecypods of the Kolchugino suite.

It is convenient to begin a preliminary characterization of our fauna with a comparison, in facies terms, of the deposits containing this fauna with analogous Upper Paleozoic formations of other regions and countries. Excluding the marine formation from consideration, we may, for the fauna-bearing Upper Paleozoic deposits, recognize the presence of two principal types of sediments, sharply differing both lithologically and faunistically. The first type is represented by red-colored and variegated, often gypsum-bearing rocks; characteristic examples of this type of deposits are the Upper Paleozoic formations of the Oka–Volga basin, the Dead Red Beds of the Middle—

of Europe and the Karoo Formation of South Africa; all the formations mentioned are of Permian age. Another type of deposits of interest to us is represented by gray and black coal-bearing rocks, in which the fauna is confined to clayey and coaly shales; characteristic examples of this type of formation are the deposits of the coal basins of Western Europe and the Donets Basin, which are of Carboniferous age. B. I. Chernyshev gave a comprehensive compilation of materials relating to the second type (27, Chapter II), which he called the Carbonicola facies (27, 66). From this compilation one sees the remarkable constancy of this facies, represented in an entirely uniform manner in the coal basins of Carboniferous age of England, France, Belgium, Germany, and in the Donets Basin.

Apparently, the second (red-colored) type of deposits is also distinguished by no lesser constancy; this constancy is revealed very clearly when comparing deposits as geographically remote from one another as the Permian deposits of the European part of the USSR and the Karoo Formation of South Africa; the homotaxial character of these deposits is shown with complete obviousness by the works of paleontologists who studied the fauna of reptiles and mollusks from both localities (3, 337—338). But I cannot agree with B. I. Chernyshev when he writes of the two types of deposits compared by us: “If petrographically these rocks are different, then in their facial conditions they are completely identical” (27, 57). The obvious petrographic and faunal differences between these two types of deposits undoubtedly serve as an expression of significant differences in the climatic and, in general, physical-geographical conditions of their formation. The Upper Paleozoic deposits containing a fauna of nonmarine pelecypods and associated with the red-colored type of deposits constitute a special facies which, for convenience of further exposition, applying B. I. Chernyshev’s method, might be called the Palaeomutela facies, after the name of the genus most widespread in this facies.¹

With respect to both types of deposits considered above, the coal-bearing deposits of the Kuzbass occupy a special position. In facial respect they are extremely close to the deposits of the Carbonicola facies. When one reads the characterization of the corresponding rocks of the Northern Basin of France, given by Pruvost (21, 176—177), one is struck by the complete coincidence with what could also have been written about our rocks. B. I. Chernyshev indicates that the rocks of the Kuzbass containing a pelecypod fauna “are indistinguishable from the Donets rocks” (27, 57). But if, therefore, in their character our deposits belong to

of the Carbonicola facies, then in stratigraphic terms (as will be clear from what follows) they must be correlated with deposits of Permian age. In other words, the fauna-bearing rocks of the Kolchugino Formation of the Kuzbass represent such a combination of facies type and stratigraphic position as permits them to be correlated both with the Carbonicola facies of the Carboniferous and with the Permian facies of Paleomutela, but does not permit them to be identified with either the one or the other.

This combination of conditions gave rise, in the first stages of the study of the fossil fauna of the Kolchugino Formation, to that erroneous direction which was expressed in incorrect determinations of a number of forms and in an incorrect determination of the age of this fauna. In fact, the complete similarity of the lithological character of the deposits of the Kolchugino Formation and of the European deposits of the Carbonicola facies evidently indicates similar physico-geographical conditions under which these deposits were formed; naturally, the fauna that inhabited these similar conditions will show—at least in its general character—a considerable similarity, which is what we in fact observe: many representatives of the Permian fauna of the Kolchugino Formation show an extremely convergent resemblance to forms of the European Carboniferous Carbonicola facies. If, in addition, we take into account the external monotony, the uniformity of the pelecypod fauna of this facies (of which more is said below), then it will become entirely understandable that the first investigators of the fauna of the Kolchugino Formation indicated, as part of this fauna, such popular Carboniferous species as Anthracomya minima (Ludw.) Hind, Anthracomya laevis Daws., Anthracomya phillipsii Will., Anthr. williamsoni Brown, and others, in accordance with which the age of this fauna was also determined as Carboniferous. In this way, a well-known discussion arose between paleophytologists and paleozoologists on the question of the age of the Kolchugino Formation, which at the present time must be resolved in favor of the former¹.

Next I must dwell briefly on the state of preservation of the fauna in my possession, mainly in order to take into account the influence of this factor on the methodology and accuracy of determinations. In comparison with similar faunas of other regions and countries, the fauna of the Kolchugino Formation shows no peculiarities with regard to the state of preservation. In the overwhelming majority of cases our material is represented by impressions and internal molds; shell valves are preserved much more rarely; the latter are usually broken by cracks into separate fragments and, during preparation, very easily fall apart; often the substance

the valves reveals recrystallization. In most cases the shells are deformed by pressure, usually completely flattened: closed shells, lying, as a rule, parallel to the bedding planes, have been transformed into thin flakes that almost do not permit internal preparation. The study of the structure of the hinge is impossible on most specimens; in those cases when the hinge has been preserved, opening it is a task requiring much time and special care. The difficulty of preparation is aggravated by the fact that in some cases the rock enclosing the fauna is strongly weathered and literally crumbles in the hands.

The rare preservation of the hinge and the flattened condition of shells and separate valves constitute a phenomenon quite usual for the fossil fauna of the Carbonicola facies; for our fauna, specimens that have preserved the hinge and the relief of the valves are rarities.

Deformation of the shell is a circumstance that always makes determination of a specimen difficult. But for the present group of fossils this circumstance acquires special significance because even undeformed shells of different species of any one genus from this fauna usually differ only in minor features. I had occasion to study the pelecypod fauna of the Kolchugino suite in parallel with the treatment of certain other groups of fossils (chiefly Devonian brachiopods), and this enabled me to feel especially clearly the external uniformity, the monotony of the pelecypods of the Carbonicola facies. It is enough to read descriptions of closely related species of the genus Anthracomya (or of any other) to see that the diagnostic specific characters are often very subtle differences (frequently relating to the outlines of the shell), with a large number of common characters and with an extremely similar general habitus of the shell. Nevertheless, establishing these subtle differences and revealing their specific significance is a necessary element in the study of the given fauna, since ignoring these slight but constant differences leads to an entirely indefinite and broad understanding of the species, which thereby loses, in particular, its significance as a stratigraphic index. A large number of examples of such broad and indefinite species can be found in the well-known monograph of Hind (10), where almost every plate presents, under a single species name, illustrations of very different specimens. For illustration I may refer to the remarks of B. I. Chernyshev concerning the species: Anthracomya curtata Brown (27, 32), Anthr. williamsoni Brown (27, 33), A. pulchra Hind (27, 35), A. wardi Hind (27, 34), A. calcifera Hind (27, 43); the same applies to the species A. minima Hind, A. phillipsii Will., and others. In the present work on the pelecypods of the Kolchugino suite, the line of a narrow understanding of the scope of the species is pursued, so

only in this case do the pelecypods of the carbonicola facies acquire stratigraphic significance, and only in this case do we approach an adequacy between the systematic units we establish and natural groups (the differences between which, of course, were not exhausted by the minor differences in shell form accessible to our study).

Having taken such a point of view, we are obliged to clarify the criteria of specific morphological characters for the given group of fossils. In other words, I consider it necessary to preface the description of the fauna at my disposal with a general characterization of the elements of organization of this group of pelecypods that are accessible for study in the fossil state, with an indication of the significance of each of them for purposes of classification. This consideration will provide the reader with material for a critical attitude toward the species established by me and described in the special part of this work. I consider it necessary to do this because the above-noted defectiveness of the material, with the external uniformity of the fauna, predetermines in every work of this kind the presence of a subjective element.

I shall begin with the most important element of the pelecypod shell—the hinge. The assertion that the structure of the hinge is the basis of pelecypod classification has become a truism. However, in determining pelecypods of the carbonicola facies the use of this element is greatly limited by the following two circumstances.

First, the hinge in these pelecypods is rarely preserved in the fossil state, and for a very large number of species it has still not been established (for example, in the genus Anthracomya the hinge is known in only three species). The fauna of the Kolchugino suite is no exception in this respect, and in the literature relating to this group there is only one indication (Yanishevsky, 1927) of the finding of an internal mold with a taxodont hinge.

Second, the pelecypods of the carbonicola facies belong to that category of lamellibranchs whose hinge is subject to extremely strong variation. A striking example of individual variability of the hinge may be furnished by the numerous illustrations of Carbonicola acuta Sow., given in Hind’s monograph on pls. V and VI¹. In this connection B. I. Chernyshev remarks: “one and the same species, on the basis of changes in the hinge, could have been split into several species” (27, 8). For pelecypods of the closely related paleomutela facies this variability of the hinge is likewise characteristic; to be convinced of this it is enough to examine the figures given by Amalitsky for the genera Palaeomutela Amal. and Oligodon Amal. I need not cite analogous examples from the Cenozoic and modern fauna.

But if the hinge apparatus, for the reasons indicated, cannot serve as a criterion for specific determinations, then for establishing the genus it retains all its significance, since in external characters certain species of different genera show great similarity. An example from our fauna may be the species Palaeomutela microdonta n. sp., externally identical with Carbonicola turgida Brown. From all that has been set forth the following conclusion follows: the hinge apparatus, because of the slight accessibility of its study in the fossil state and because of great individual variability, in the study of pelecypods of the Carbonicola facies cannot serve as a criterion for specific determinations, but is the most important criterion for generic determinations.

Other details of internal structure (pallial line, muscle scars, position and character of the ligament, etc.) are so rarely observed in the fossil state among pelecypods of the Carbonicola facies that they cannot have substantial importance in specific determinations, although, of course, they require careful study and recording in those rare cases when their observation is accessible to the investigator.

From the foregoing it follows that, in specific determinations of pelecypods of the group that interests us, the paleontologist must of necessity devote primary attention to the study of external characters. But precisely here the influence of subsequent deformation of the shells must be taken into account; to illustrate at once the role of this factor, I shall give an example from our fauna, analyzed in detail in the special part of this work: shells of species as different as Posidonomya subovata and Palaeomutela microdonta, when crushed, display such considerable similarity that in some cases distinguishing them seems to me impossible (if, of course, elements of the hinge have not been preserved).

Let us consider the role of the various external characters of the shell in the determination of pelecypods of our facies.

Sculpture of the outer surface of the shell, which plays a very prominent role in the diagnosis of those groups in which this sculpture shows considerable diversity, has a very modest significance in the specific determinations of our fauna. The chief reason for this is the uniformity and simplicity of the sculpture in pelecypods of the Carbonicola facies. And if Pruvost asserts (21, 188) that, given sufficient preservation of the outer layer of shells, even from fragments of the latter one can make generic determinations (for the genera Carbonicola, Anthracomya, and Naiadites) on the basis of the character of the periostracum, then specific differences in the sculpture of the shell, as a rule, are not expressed. “The shell is covered with concentric wrinkles and fine growth marks,” “the shell is covered with fine concentric lines”—such and similar are the usual formulas that we find in descri-

of almost every species, for even the most attentive investigator can make any additions to these standards only for a few species. If one adds to this that the sculpture, while remaining essentially uniform, shows slight variations on the nuclei, shell, and impressions of one and the same species, and that it is subject to equally slight fluctuations in connection with deformation of the shell, then we must conclude that, in species determinations, this element is in most cases indifferent.

The relief of the valves provides important diagnostic elements for many species. But, unfortunately, it is precisely the relief of the valves that is affected first of all by deformation of the shells. Not to mention the very common case in which the shells prove to be completely flattened, even slight compression of shells entails the loss of one or another feature of the relief of the valves. For our fauna this circumstance must be noted especially, since the number of undeformed specimens is extremely limited, while the usual type consists of shells that are completely flattened.

The dimensions of shells can enter into species diagnoses only in rare cases; the majority of pelecypods of the Carbonicola facies are shells of medium size, and shells similar in their characters but differing in dimensions in most cases mark only age stages. However, some species show excessively sharp deviations in one direction or another (among ours, for example, Palaeomutela (?) nanella), and in such cases absolute dimensions are not indifferent.

The outlines of the shell are of very great interest for species determinations, since in the outlines there is observed a large number of variations which, though usually inconspicuous, are nevertheless stable: the position of the beaks, the length of the hinge margin, its connection with the anterior and posterior margins, the presence or absence of a sinus on the ventral margin, the convexity or straightness of the posterior margin, the magnitude of the upper posterior angle, etc.—these are the elements whose different variations and different combinations, taken together, characterize each species with sufficient precision. Of course, the outlines of the shell can be characterized most accurately from an undeformed specimen; but study of the collection available to me allows me to note that crushing entails a sharp change in outline only in markedly convex forms, whereas in species possessing a slightly convex shell (as, for example, in species of the genus Anthracomya), uncrushed specimens show almost complete agreement in outline with crushed specimens (provided only—what is typical of our fauna—that the crushing force was oriented normal to the plane of symmetry of the shell).

Table

for determining the representatives of the genus Anthracomya Saltre described in the present work.

Note. The figures in parentheses following the species names indicate pages on which a detailed description of the corresponding forms is given.

1. Ventral margin convex throughout . . . . . . . . . . . . . . . . . . . . . . 7
   — Ventral margin with a sinus, straight or straightened in the middle part . . . . 2

2. Ventral margin has a weakly expressed sinus. Shell developed diagonally, subtriangular in outline; hinge margin long; beaks strongly approximated to the anterior margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Anthracomya trigonalis n. sp. (55).

— Ventral margin straight or straightened in the middle part . . . . . . . . . . 3

1. Shell developed diagonally—strongly narrows toward the anterior end and widens backward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   — Shell developed in the direction of its length; hinge line subparallel to the ventral margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2. Ventral margin straight in the middle part. Posterior margin broadly rounded, smoothly adjoining the strongly convex margins; beak occupies an almost terminal position; $\beta = 30^\circ$ . . . . . . . . . . . . . . . . . . . . . . . .

Anthracomya sp., cf. A. wrighti Dix et T. (54).

— Ventral margin completely straight. Outlines of the shell wedge-shaped . . . . .

Anthracomya n. sp. (70).

1. Hinge margin very long (more than 3/4 of the length of the shell); posterior dorsal angle small (less than 130°). Hinge and ventral margins almost parallel; posterior margin convex, sometimes straightened in the middle part; beaks strongly displaced toward the anterior margin . . . . . . . . . . . . . . . .

Anthracomya subparallela n. sp. (60).

— Hinge margin short (equal to or slightly more than 1/2 the length of the shell); posterior dorsal angle greater than 140° . . . . . . . . . . . . . . . . . 6

1. Posterior margin straight. Posterior end very long, drawn backward and downward; anterior end, owing to the almost terminal position of the beaks, very small; ventral margin straight almost throughout; hinge margin makes up 1/2 the length of the shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Anthracomya porrecta n. sp. (56).

— Posterior margin convex. Ventral margin straightened only in the middle part; posterior end long, anterior short; beaks strongly approximated to the anterior margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Anthracomya similis n. sp. (62).

1. Shell developed diagonally (angle between the hinge margin and the direction of the ventral margin considerable) . . . . . . . . . . . . . . . . . . . . . . 8
   — Shell developed lengthwise (angle between the hinge margin and the direction of the ventral margin insignificant) . . . . . . . . . . . . . . . . . . . . . 11

2. Posterior margin straight or straightened in the middle part . . . . . . . . . . 9
   — Posterior margin convex throughout . . . . . . . . . . . . . . . . . . . . . 10

3. Posterior margin straight in its upper and middle parts, forming a distinct angle with the hinge margin; posterior end long, drawn downward; anterior end small—beaks strongly approximated to the anterior margin; angle $\alpha$ less than 150° . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Anthracomya supraphilipsii n. sp. (49).

— Posterior margin straightened in the middle part, smoothly adjoining the hinge margin (angle between them rounded); posterior end short and broad; shell very high (height reaches 3/4 of the length); angle $\alpha$ small (about 110°) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Anthracomya lata n. sp. (68).

1. Outlines of the shell regularly elliptical—the hinge margin is slightly curved and quite smoothly adjoins the regularly convex posterior margin; angle $\alpha$ rounded, its value about 150; beaks strongly approximated to the anterior margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Anthracomya tschernyschewi n. sp. (52).

— Outlines of the shell obliquely triangular—the hinge and posterior margins (often almost equal in length) form two sides of a triangle with rounded angles between them of about 125°; the third side is the convex ventral margin. Beaks remote from the anterior margin by less than 1/4 the length of the shell. Dimensions small . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Anthracomya obliqua n. sp. (58).

1. Posterior margin rounded . . . . . . . . . . . . . . . . . . . . . . . . . . 12
   — Posterior margin straight . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2. Posterior half of the shell considerably wider than the anterior. Hinge margin long (about 3/4 of the length of the shell); upper dorsal angle small (100–120°) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Anthracomya n. sp., cf. A. curtata Brown (69).

— Shell widens backward very insignificantly—in the anterior half the shell has the same height as in the posterior . . . . . . . . . . . . . . . . . . . . 13

1. Ratio of height to length of shell about 3/5. Shell of oval outline; hinge margin, making up 2/3 of the length of the shell, smoothly adjoins the anterior and posterior margins; beaks remote from the anterior margin by 1/4 the length of the shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Anthracomya fedotovi n. sp. (63).

— Ratio of shell height to length considerably less than or considerably greater than 3/5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

1. Ratio of shell height to length about 1/2; outlines of the shell oval; hinge margin, making up somewhat more than 1/2 the length of the shell, smoothly adjoins the anterior and posterior margins; beaks remote from the anterior margin somewhat more than 1/5 the length of the shell . . . . . . . . . . . . . . . .

Anthracomya fedotovi n. var. producta (64).

— Ratio of shell height to length more than 3/4; outlines of the shell oval; hinge margin, making up 1/2 the length of the shell, smoothly adjoins the anterior and posterior margins; beaks remote from the anterior margin less than 1/5 the length of the shell . . . . . . . . . . . . . . . . . . . . . . .

Anthracomya fedotovi n. var. lata (80).

1. Posterior dorsal angle not rounded, its magnitude—125°; beaks remote from the anterior margin by a distance equal to 1/5 the length of the shell; hinge margin long . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Anthracomya tomiensis n. sp. (65).

— Posterior dorsal angle rounded, its magnitude about 110°; beaks remote from the anterior margin by a distance equal to 1/3 the length of the shell; hinge margin long . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Anthracomya simplex n. sp. (67).

Finally, a few remarks concerning the structure of the shell substance and the thickness of the valves. In the specimens I have, belonging to different forms, I was able to observe certain differences in the structure of the valve substance. Thus, in shells of Palaeomutela there is usually observed a radial-fibrous structure, producing on the outer surface and on its impressions the appearance of the finest radial striation. I did not observe a similar structure in representatives of other genera. Thus the structure of the shell substance may prove to be a character of importance for generic determinations, but in this matter it is first necessary to clarify the character and influence of recrystallization of the shells, which inevitably must have affected their structure. As for the thickness of the valves, generic differences are also observed in this respect; thus, the shell in the genus Palaeomutela is considerably thicker than in the genus Anthracomya; but I observed no differences of this kind for species belonging to a single genus.

Thus we arrive at the following conclusions: species determinations of pelecypods of the Carbonicola facies are based on external characters; for the fauna of the Kolchugino suite, of these characters the details of the outline of the shell are of especial importance; the differences between species are often very slight, at least in fossil material.

The latter circumstance compels one to draw yet another conclusion, now concerning the description of species: descriptions must be detailed and exhaustive. Strictly speaking, this requirement should be made of any paleontological work, but failure to observe it leads to the most regrettable results precisely in descriptions of groups such as our pelecypods. Schematic, incomplete descriptions of species, or references such as “our specimens do not differ in any way from such-and-such,” make it almost impossible to use the corresponding literature, since they often do not make it possible to determine what content the author assigned to one or another specific name. Unfortunately, precisely such is the small body of literature that has been published up to the present on the Kolchugino pelecypods¹. It must be stated that even for those species whose names have already gained currency and are cited in every work, there are no even approximately exact diagnoses or, to any degree, detailed descriptions.

In the present work I have endeavored to give detailed descriptions of the species I have determined not only in order to give the reader an exact idea of the scope of each species as accepted by me, but also because, working in Siberia, I have not had the opportunity to become acquainted with certain of the latest literary data relating to my subject. Therefore, not

it is not impossible that a researcher working under more favorable conditions will find himself compelled to introduce certain corrections into my definitions; in that case it is necessary that the material at my disposal be characterized by me as fully as possible. For this same purpose, at the end of the description of each species an exact enumeration is given of the described specimens, which are kept in the Paleontological Cabinet of the Tomsk Industrial Institute named after S. M. Kirov.

In describing each species I give a table of the ratios of the various metric elements of the shell; I am not inclined to exaggerate the significance of these ratios and I know that they are not entirely objective, since some elements cannot always be measured with sufficient accuracy (for example, the length of the hinge margin, when it passes smoothly into the anterior and posterior margins, or the magnitude of the posterior dorsal angle, when the posterior margin has considerable convexity). But I have had the opportunity to convince myself that these ratios in a number of cases are useful additions to the diagnosis. For the measured elements of the shell I have adopted the following designations.

Fig. 1.         Fig. 2.         Fig. 3.

Genus Anthracomya Salt. (fig. 1):

L — the greatest measurement in length, taken parallel to the hinge margin;

l — length of the hinge margin;

l′ — distance from the anterior margin to the beak, measured parallel to the hinge margin;

H — greatest height of the shell, measured perpendicular to the hinge margin;

h — height of the shell passing through the beak;

α — posterior dorsal angle;

β — angle between the direction of the ventral margin and the hinge line.

Genus Posidonomya Bronn (fig. 2):

L — greatest length of the shell;

l″ — length of the posterior (straight) part of the hinge margin;

l′ — distance from the anterior margin to the beak;

H — greatest height of the shell;

γ — angle at the beak.

Genus Palaeomutela Amal. (fig. 3):

L, l′, H, and γ have the same meanings as in the preceding case.

For all genera these elements are connected by the relation:

\[ L \parallel l \parallel l' \parallel l'' \perp H \parallel h \]

The literature on pelecypods of the Kolchugino Series is not large. Venyukov in 1894 indicated (according to the determinations of Amalitsky) the presence, in deposits of this series developed in the Leninsk district, of the species Posidonomya becheri Bronn and Carbonicola carbonaria Goldf. (30, 86). In 1901 there appeared a note by Jones (12) on pelecypods from the Kolchugino deposits developed along the V. Ters River, consisting of 3 pages of text and one plate of illustrations; in this work our fauna was characterized for the first time, but, in accordance with the size of the note, only extremely schematic characteristics of the following forms were given:

Anthracomya minima Ludw.
” laevis Daws.
” laevis Daws., var.
” valenciensis Ether.
Posidonomya subovata n. sp.
” concinna n. sp.

In 1934 Hind, in describing Edmondia punctatella, touched upon the question of the generic affiliation of the species Posidonomya subovata Jones, speaking against assigning it to the genus Posidonomya Bronn (11, 148). “At a later time (1923) A. A. Stoyanov touched upon the fauna of interest to us; he cited from the coaly shales in the vicinity of the village of Erunakova Anthr. phillipsii Will., Anthr. laevis Daws., Anthr. minima Hind, and the author emphasized the joint occurrence of this fauna, including A. phillipsii, which is characteristic of the upper part of the Coal-Measures of England, with well-preserved representatives of Noeggerathiopsis aequalis. In addition, from the Kolchugino beds Stoyanov cites N. aequalis together with Parallelodon angustus Hind, ‘a form occurring even in the Lower Carboniferous of England’.” (I quote after Yanishhevsky, since Stoyanov’s work is not at my disposal).

Grabau, in his summary on the stratigraphy of China, touched upon the question of the occurrence in the Erunakovo and Kolchugino deposits of Carboniferous species indicated by Stoyanov; he expressed himself on the possibility of migration of these forms from Europe into Siberia and of their existence in Siberia in Permian time (9, 404). Doubt as to the correctness of identifying the Kuznetsk pelecypods with European ones and as to the Carboniferous age of the former was also expressed by Zalessky (34).

Yanishhevsky in 1927 published an article (32) on the fauna of the Kolchugino Series: in this article the presence is indicated, in the deposits of this series developed in the Leninsk district and in the basin of the Upper Ters, of the species Anthracomya minima, Anthracomya williamsoni, Posidonomya subovata, Posidonomya (?) concinna;

descriptions of these species are not given, but illustrations are provided; moreover, the image of Posidonomya (?) concinna Jones (32, pl. I, fig. 10) is the first document from which the characters of this species can be established, since Jones did not describe this species, and his illustration of it is unsatisfactory. In the work of Yanishevsky we first find an indication of the presence, among the Kolchugino pelecypods, of forms with a taxodont hinge.

In recent years a number of works by Ragozin have appeared, devoted to the pelecypod fauna of the coal-bearing series of Kuzbass (22, 23, 24). In the first of these works the author quite decisively identified the Kuzbass pelecypods with European Carboniferous forms (Anthr. phillipsii, Anthr. minima, Anthr. pulchra, etc.), but later he adopted the view that the lamellibranch fauna of Kuzbass is entirely endemic, not only with respect to its species composition but also to its generic composition.

Proceeding from the preconceived assumption that in the coal-bearing deposits of Kuzbass there can be not only no species, but also no genera, in common with the corresponding fauna of Europe, Ragozin in his works establishes a number of new genera, without, however, giving them exhaustive diagnoses and without providing comparisons with already described genera of pelecypods of this facies. In the collection studied by me I did not find a single genus that was not already known from the Carboniferous or Permian deposits of Europe.

[In 1937 a work by Fedotov appeared in print, devoted to the pelecypod fauna of the coal-bearing deposits of Kuzbass; in this work, along with the description of pelecypods from the Balakhon and Bezugolnaya series, the author describes 12 forms from the Kolchugino suite; all the forms are native or new. For the first time, representatives from Kuzbass of the Permian genera Palaeanodonta Amal., Palaeomutela Amal. are described in print and—with a question mark, since the hinge remained unstudied—Oligodon Amal. The list of species established by Fedotov is:

Anthraconauta iljinskiensis Fed.
Anthraconauta pseudophillipsii Fed.
Anthracomya gapeevi Fed.
Palaeomutela sp. n.
Palaeanodonta kuznetskiensis Fed.
Palaeanodonta cf. longissima Netsch.
Palaeanodonta tersiensis Fed.
Oligodon (?) plotnikovskiensis Fed.
Abiella concinna Jones
Abiella concinna Jones var. angustistriata Fed.
Abiella subovata Jones
Abiella tomiensis Rag.

One year later, 7 of these 12 forms are cited by Fedotov in another work devoted to the description of the fauna from cores].

On the Generic and Specific Composition of the Pelecypods of the Kolchugino Formation

The composition and general character of the pelecypod fauna of the Kolchugino Formation are determined by that combination of the stratigraphic position and the facies character of the deposits of this formation which has been clarified in detail above (p. 20). Thus, among representatives of the genus Anthracomya there are species that show an extraordinary convergence with Carboniferous European forms. On the other hand, in our fauna there are representatives of the genus Palaeomutela, which is absent from the European deposits of the Carbonicola facies, but is, however, widely distributed in red-colored Permian rocks.

The generic composition of the pelecypods of the Kolchugino Formation has not yet been established with sufficient precision. The absence of monographic studies of this fauna and the difficulty of studying the hinge are the reason why many generic determinations may give rise to doubts and serve as grounds for discussion.

In various authors one may find the following generic groups established by them in the Kolchugino fauna: Carbonicola (Amalitskii, 1894), Anthracomya (Jones, 1901; Stoyanov, 1923; Yanishevsky, 1927; Ragozin, 1931), Posidonomya (Amalitskii, 1894; Jones, 1901; Yanishevsky, 1927; Ragozin, 1931). For each of these genera, materials relating to the fauna of the Kolchugino Formation are presented below. [Fedotov (1937) gives the genera: Anthracomya, Anthraconauta, Palaeonodonta, Palaeomutela, Oligodon (?), Abiella.]

Carbonicola M’Coy.

This genus rarely appears in lists of fossil pelecypods of the Kuzbass. From the Kolchugino Formation, Amalitskii in 1894 identified Carbonicola carbonaria Goldf. (30, 86); considerably later, from the same formation, Ragozin described a form under the name Carbonicola acuta (22, 9), which he later referred, with a question mark, to the genus Anthracomya, and still later—to his new genus Prokopievskia (23,317). In our fauna representatives of the genus Carbonicola M’Coy are absent, but some species of the genus Palaeomutela show complete external similarity to European species of Carbonicola. Probably, to the genus Palaeomutela

belongs also the specimen defined by Amalitsky as Carb. carbonaria. As for Ragozin’s specimen, it evidently belongs to the genus Anthracomya Salt.

Anthracomya Salt.

To this genus belong the majority of the pelecypods of the Kolchugino series. Jones identified among this fauna A. minima Ludw., A. laevis Daws., A. laevis Daws. var. and A. valenciensis Ether. Stoyanov added to this list A. phillipsii Will., and Yanishevsky—A. williamsoni Bronn. In the present work I have assigned 16 forms to the genus Anthracomya.

Very many pelecypods of the Kolchugino series, in all their characters, show complete similarity to the genus Anthracomya. This similarity is so great that a number of authors directly identified many Kolchugino pelecypods (as is evident from the list given above) with previously described species of this genus. Thus, even with the hinge unstudied, one can hardly doubt the presence of the genus Anthracomya in the Kolchugino fauna. However, in making this statement, I must supplement it with two observations.

The first of these concerns the genus Palaeanodonta, established by Amalitsky in 1895 for those edentulous Permian forms which he had previously assigned to the genus Najadites. Taking into account, in general, the poor study of the hinge in representatives of the genus Anthracomya (see p. 22), its weak development in this genus and its extreme variability in freshwater and lagoonal pelecypods even within a single species, as well as the fact that the hinges of the Kolchugino pelecypods have not been studied, I have not found satisfactory criteria for distinguishing the genera Palaeanodonta and Anthracomya in the Kolchugino fauna, given its present state of study. The posterior expansion of the shell, characteristic of many representatives of the genus Anthracomya, is not, however, a universal character, and a number of forms from the European Carboniferous fauna may be cited that are assigned to the genus Anthracomya but possess a maximum height passing approximately through the middle of the hinge margin. On the other hand, Permian representatives of the genus Palaeanodonta possess such varied outlines that to rely on external characters for distinguishing these genera appears extremely difficult. Among the Kolchugino pelecypods, alongside a large number of forms possessing typical Anthracomya outlines, there are also some that may be compared with certain palaeanodonts. But only one specimen, showing an almost complete similarity to the species Palaeanodonta castor Eichw., I considered it possible to assign to Amalitsky’s genus.

The other observation will concern representatives of the group Anthracomya phillipsii; this group was separated by Pruvost into the genus Antraconauta, but I have been unable to examine the corresponding materials in the original source. Therefore I

I leave the pelecypod of the group Anthr. phillipsii within the genus Anthracomya¹.

Thus, in the present work the genus Anthracomya is given a broad scope, and it is quite possible that, upon further detailing, some of the species included by me in this genus will be assigned to Anthraconauta and Palaeanodonta.

Among the 16 forms of the genus Anthracomya described by me in this work, many show considerable similarity to European Carboniferous species. Thus, for example, the species A. supraphillipsii and A. tshernyschewi have their closest analogues among those rather diverse forms which, by various authors, are described under the name Anthr. phillipsii Will. Anthr. similis is rather close to Anthr. williamsoni Bronn. Anthracomya lata in some respects strongly recalls Anthr. laevis Daws.; Anthr. simplex shows considerable similarity to certain representatives of Anthr. subcentralis Hind. But in all these cases our species display one or another difference, which is noted in the descriptions of these species and which, in view of the considerable difference in stratigraphic position, obliges one to separate the Kolchugino forms from the European ones. In several cases, when I was dealing with single specimens that did not permit comprehensive study, I had to confine myself merely to indicating their similarity to one or another European species; such are the specimens described under the name Anthracomya sp., cf. A. wrighti Dix et Truеm.; Anthracomya sp. cf., Anthr. curtata Brown. In all probability, these specimens too represent new forms.

Thus, despite their external similarity, the anthracomyae of the Kolchugino Series belong to species that have not previously been described and had to receive new names in this work. I consider it useful, for the Kolchugino anthracomyae, detailed descriptions of which are given below, to provide a dichotomous table. (See below.)

There are also certain general features of the anthracomya fauna of the Kolchugino Series which distinguish it as a whole from the anthracomya fauna of the European Carboniferous. First, among the anthracomyae present in our collection there are no² forms possessing a sinus on the ventral margin: in the overwhelming majority of species the ventral margin is regularly rounded; more rarely it is straight (Anthr.

cf. wrighti, Anthr. porrecta and some others). True, the form depicted by Yanishevsky (32, 1016) under the name Anthr. williamsoni has a distinct sinus on the ventral margin, but, apparently, such forms occur comparatively rarely, since otherwise it would be difficult to explain their absence in our rather extensive collection¹. Another conspicuous feature of our anthracomyiids is the absence among them of forms with a long anterior end tapering forward, characteristic of such groups widespread in Europe as the group Anthr. modiolaris, the group Anthr. williamsoni, etc. In the overwhelming majority of our anthracomyiids the umbones are strongly shifted toward the anterior margin, and the anterior end is short and broad. But even in those few species (Anthracomya obliqua, Anthracomya fedotovi) in which the umbones are considerably removed from the anterior margin, the anterior end is blunt and broadly rounded.

If the differences between the Kolchugino anthracomyiids and the European Carboniferous species are explained by differences in stratigraphic position, and the differences from the Permian species by differences of facies character, then the causes of the differences between the anthracomyiids of the Kolchugino Formation and the anthracomyiids of the coal-bearing deposits of the Minusinsk Basin are less clear: among our 16 forms, representatives of six species of anthracomyiids described by B. I. Chernyshev from the Minusinsk depression (26) are entirely absent. I also lack such forms as would be close or identical to the two Chinese species schematically characterized by Grabau (9). It must be supposed that the reason for these differences between the Kolchugino anthracomyiids and representatives of this genus from the Permian deposits of other regions of Asia lies in the different stratigraphic position of the corresponding deposits within the Permian system: a rapid replacement, in the vertical direction, of some species of anthracomyiids by others is clearly traceable even within a single Kolchugino Formation.

Palaeanodonta Amal.

This genus, established in 1895 by Amalitsky (3, 346) for forms previously assigned by him to the genus Najadites, has not so far been found in the coal-bearing deposits of the Kuzbass². As already noted above, some of our anthracomyiids (as, for example, Anthr. tschernyschewi, which has an oblique hinge margin) may prove to belong to this genus. However, typical palaeanodonts, with a shell tapering backward and an oblique hinge margin (3, 237), are not present in our collection. But, on the other hand,

there is one specimen which, by its external features, is scarcely distinguishable from certain representatives of the species Palaeanodonta castor Eichw., which is the genotype of the given genus. This specimen is described in detail below under the name Palaeanodota sp., cf. P. castor.

Posidonomya Bronn.

This genus was first identified in the fauna of the Kolchugino series by Amalitsky, who found, among Venyukov’s material, the species Posidonomya becheri Bronn. None of the later authors has confirmed by his determinations the presence of this species among the pelecypods of the Kolchugino series, and it remains unclear what form was assigned by Amalitsky to Bronn’s species. In 1901 Jones assigned to the genus Posidonomya two new forms from the Kolchugino deposits of the Upper Ters, naming them Posidonomya subovata and Posidonomya concinna; the specimens that were at Jones’s disposal and were figured by him with only very schematic characteristics were crushed, deformed shells that showed no convincing generic characters of Posidonomya. Hind pointed out (11, 148) the considerable similarity of Jones’s figures of P. subovata to Edmondia punctatella and spoke decisively against assigning Jones’s Kolchugino species to the genus Posidonomya.

Much later, Yanishevsky, citing Hind, expressed doubt as to the belonging of the species concinna to the genus Posidonomya, but left subovata within this genus; as we shall see below, such a solution of the question corresponds to what I was able to observe also in my own material. In 1931 Ragozin, together with the species concinna and subovata, described a new species, tomiensis, which he also assigned to the genus Posidonomya, but in his most recent work he already assigns all these species to his new genus Abiella.

At my disposal there is a large number of specimens representing crushed, deformed shells, no different from Jones’s figures of subovata. But alongside these specimens, whose belonging to the genus Posidonomya was doubtful, I have about two dozen specimens of well-preserved, undeformed valves, very typically expressing the characters of the genus Posidonomya. In particular, the outlines of the hinge margin are very typical—a small, rounded anterior auricle and a more developed, flat posterior auricle, bounded above by a straight hinge margin (see Figs. 24–25); the hinge margin is toothless; for these suboval shells, slightly widening backward and somewhat developed in length, I retain the name Posidonomya subovata Jones, giving this species, on the basis of the study of undeformed shells, a new diagnosis.

The imperfection of the figures and the absence of descriptions of the species concinna and subovata by their author led to extreme confusion regarding their systematic position. On the basis of the study of the material available to me, I came to the conclusion that the species subovata belongs to the genus Posidonomya, whereas the species concinna belongs to some genus of equivalved pelecypods, most probably to the genus Palaeomutela.

D. M. Fedotov holds another point of view, referring both these species, as well as the species tomiensis Rag., to the genus Abiella Rag. In this connection I consider it necessary to make a number of remarks.

First of all, I must note that I do not consider it possible to assign these three forms to a single genus. This, however, follows directly also from the descriptions given by D. M. Fedotov. In a work published in 1937, this author writes (p. 44): “I can also note a certain convergent similarity in the external sculpture in the Kuznetsk concinna (pl. IX, fig. 11) and Posidonomya becheri Bronn. (Weigelt, pl. 8, figs. 1—4). However, the entire architecture of the shell of concinna, subovata, and of tomiensis, which is close to the latter, gives no grounds for keeping them within the genus Posidonomya. It can only be noted that in very young specimens of concinna and subovata the shell has an almost round form, with a rounded central prodissoconch, whereby they partly recall the early growth stages of Carboniferous and Jurassic representatives of the genus Posidonomya (Weigelt, pp. 72, 73, 74), but whereas in the course of individual growth the shell of true Posidonomya acquires the characteristic features of representatives of the family Aviculidae Frech., i.e., forms of the group Monomyaria or Heteromyaria, the Kuznetsk pelecypods retain the typical structure of Dimyaria. No tendencies toward the acquisition by them of characters of the family Aviculidae, to which such well-known forms as Avicula Brng., Leiopteria Hall, Pseudomonotis Beirych and others belong, appear either in concinna, or in subovata, and still less in tomiensis.” But already in 1938, on the basis of the study of material of better preservation, the cited author comes to a different conclusion (1938, p. 240): “There is no doubt that in these representatives of Abiella concinna the characters of the genus Posidonia Bronn = Posidonomya Bronn are expressed rather clearly. If in them the posterior part of the shell were more convex and more projecting, the type of the genus Posidonia Bronn—Posidonomya Bronn (Weigelt, 1922, or Zittel, 1934, p. 613) would be fully expressed. The features of the order Anisomyaria are clearly expressed in this Kuznetsk form; it now becomes understandable why Jones (1901, p. 43) assigned his species concinna to the genus Posidonomya.”

I have cited these two excerpts in order to show, by the example of another author’s investigations, how strongly the appearance of the shells of our fauna changes depending on the state of preservation—an circumstance that must constantly be borne in mind and that I illustrate below by comparing the shells of such different forms as Posidonomya subovata and Palaeomutela microdonta.

To this it must be added that among the group of species of interest to us, referred by D. M. Fedotov to the genus Abiella, there are forms “with a straight, long, strongly developed margin” (43, 239) and forms in which the hinge margin is “almost straight” (42,51); the former belong to Anisomyaria, the latter to Dimyaria, as will be shown by me below. The assignment of these forms to the genus Abiella, which has neither a satisfactory diagnosis nor comparisons with other genera, I do not consider possible, and I fully agree with the remark “on the necessity of re-examining the species of the genus Abiella and revising the genus itself” (43, 240).

The species subovata is not the only representative of the genus Posidonomya in our fauna; besides it, there is one more peculiar form, just as clearly expressing the characters of the genus Posidonomya and named by me Pos. linguloides because of a certain resemblance of the almost equilateral shell of this species to the known genus of inarticulate brachiopods.

As for Jones’s second species—concinna—it has not yet been possible to establish precisely to which genus it should be assigned, but there are apparently no grounds for leaving it within the genus Posidonomya (see below).

Palaeomutela Amal.

This genus, so widely distributed in the Permian deposits of Europe and South Africa, had until now not been known in the fauna of lamellibranchs of the productive series of the Kuzbass. In my collection there are rather many pelecypods whose shells, in an unetched state, are externally scarcely distinguishable from certain Carboniferous species of the genus Carbonicola. However, by etching with hydrochloric acid I was able to establish that they possess a taxodont (or pseudotaxodont) hinge, on the basis of which I assigned them to the genus Palaeomutela. The hinge of these specimens consists of a series of extremely small, rather even denticles directed almost perpendicular to the line of the hinge margin; one artificially obtained internal mold

\[ \frac{\mathrm{XXIIIA}}{256} \]

shows on the hinge margin, behind the beak, about 30 such denticles. This hinge shows the greatest similarity to the hinges of the species Palaeomutela umbonata Fisch., judging from the drawing given by Nechaev. On other specimens (for example,

\[ \frac{\mathrm{XXIIIA}}{13a} \]

) these denticles are less regular, but, apparently, in general the Kolchugino specimens possess more numerous, small, and regular denticles than most European representatives of the genus Palaeomutela. However, taking into account the general variability of the hinge in the group of pelecypods under consideration and, in particular, in species of the genus Palaeomutela, I considered it possible to describe the Kolchugino specimens under the name Palaeomutela microdonta, although perhaps the specific name of this form should have been applied as a generic one for our forms, which possess extremely small hinge denticles, distinguishable with difficulty without considerable magnification. All the specimens in which I have established the hinge characterized above belong to one new species, named by me Palaeomutela microdonta and described in detail below.

[The hinge in the Kuzbass representatives of the genus Palaeomutela I observed on several artificially obtained molds, which conveyed its structure quite distinctly—numerous small denticles of taxodont type.

D. M. Fedotov described in 1937, from the coal-bearing deposits of the Kuzbass, Palaeomutela n. sp. from the Kolchugino suite and Palaeomutela (?) astartellaeformis Fed. from the barren suite. The structure of the hinge in these forms is characterized in the following expressions: Palaeomutela n. sp.: “The hinge margin is thickened in the form of a ridge and bears irregular denticles and pits… Owing to the poor preservation it is very difficult to describe the structure of the hinge with certainty; nevertheless the irregular projections and pits, visible on the thickened margin of some specimens, apparently are parts of the dental apparatus” (42, 22).

Palaeomutela (?) astartellaeformis: “The hinge consists of many small denticles situated behind the beak… if the structure discovered by me on the upper margin and resembling small denticles of the hinge apparatus of the genus Palaeomutela is indeed a part of the hinge apparatus, then the resemblance of our form to the genus Astartella is purely external. In that case the Kuzbass form must be assigned to the genus Palaeomutela” (42, 21).

The caution in characterizing the hinge of these forms is fully justified by the condition of those specimens which served D. M. Fedotov for establishing

of the species under consideration, and with which I was able to acquaint myself in the Central Museum of the Central Scientific-Research Geological Prospecting Institute in Leningrad. On the basis of this examination I came to the conclusion that the hinge margin of specimens bearing the label “Palaeomutela n. sp.” (illustrated on Plate VII, figs. 8, 9) shows no similarity whatever to the hinge margin of our Palaeomutela; the “pits and denticles” of these specimens seem to me to be doubtful formations, as is the assignment of these specimens to the genus Palaeomutela.

Only in one specimen of Palaeomutela astartellaeformis (illustration—42, Plate II, fig. 5; museum number—39) could I discern traces of small denticles, recalling the hinge of Palaeomutela microdonta, but in an extremely imperfect state of preservation.

On the other hand, among the numerous specimens of D. M. Fedotov’s collection bearing the label “Abiella subovata,” many, in my opinion, belong to the genus Palaeomutela, namely to the species Palaeomutela microdonta mihi (see p. 72).

Besides Palaeomutela microdonta, in the collection studied by me there are three further forms whose hinge could not be detected and whose generic affiliation has not been precisely established; but in external characters these species show the greatest affinity to Palaeomutela microdonta, for which reason they are provisionally assigned to the genus Palaeomutela. These species are the following:

Palaeomutela (?) concinna Jones.
Palaeomutela (?) tomiensis Rag.
Palaeomutela (?) nanella n. sp.

The species concinna was so incompletely characterized by its author that I had to accept as the hypotype of this species the specimen figured by Yanishevsky (32, Plate I, fig. 10) under the name Posidonomya (?) concinna. Similar specimens, though in small number and of poor preservation, were found by me among the fauna described below. On these specimens I could not detect characters that would allow them to be referred to the genus Posidonomya; on the contrary, the outlines of their shell, tapering backward, bring them closer to such genera as Palaeomutela, although, of course, until the hinge of these specimens has been studied, their systematic position will remain uncertain.

[Another interpretation of the species concinna is given by D. M. Fedotov. The forms described by him under the names Abiella concinna and Abiella concinna var. angustistriata (the specimens named by this author Pseudomonotis (?) sp. also belong here) belong to the subclass Anisomyaria: “the characters of the order Anisomyaria are clearly expressed in this Kuznetsk form” (43, 240). These specimens differ substantially from the one figured under the name Posidonomya (?) concinna by M. E. Yanishevsky and which, for the reasons set forth above, I take as the hypotype of the species concinna. In my collection there were only specimens similar to the indicated specimen of M. E. Yanishevsky, which I saw in the TsNIGRI museum—it (museum No. 18) is somewhat damaged since the time when its photograph was placed in the work of M. E. Yanishevsky, but nevertheless it reveals clearly enough those features which compel me to regard it as a representative of a species of the subclass Dimyaria. A good impression of another specimen (left valve) of the same species is present on specimen 18a, beside a larger impression of a shell belonging, apparently, to the species “Abiella concinna” in D. M. Fedotov’s understanding. The differences between these forms are so considerable that I cannot regard them merely as differences of age. Thus it must be stated that, under the names respectively Posidonomya (?) concinna and D. M. Fedotov’s ...]

and Abiella concinna substantially different forms are depicted; moreover, owing to the absence of a description and the imperfection of Jones’s figure, it is difficult to decide which form—Yanishevsky’s or Fedotov’s—is closer to Jones’s original. Under these conditions, it would probably be most correct to abandon the use of the name “concinna” as having lost all definiteness. If, however, this name is retained, then its application is possible to two different forms:

1—The species name “concinna” applies to the specimens described and figured by Fedotov; in this case the species concinna remains within the genus Posidonomya, while the specimens of Yanishevsky (and mine) must receive a new species name;

2—The name “concinna” is retained for Yanishevsky’s specimens (and mine); in this case the species concinna cannot be left within the genus Posidonomya, and Fedotov’s specimens must receive a new species name.

Likewise, provisionally, in view of the insufficient study of the hinge, Ragozin’s species tomiensis is assigned to the genus Palaeomutela; its shell possesses characteristic elliptical outlines, a non-straight hinge margin, and a high, almost centrally situated umbo¹). The new species nanella, in the general habitus of the shell, stands closest (among the Kolchugino pelecypods) to the genus Palaeomutela.

In conclusion I must add that I have repeatedly had occasion to observe how greatly the outlines of the shell change in forms assigned by me to the genus Palaeomutela when they are compressed. In a number of cases I was unable to determine compressed specimens, and I suppose that, given the present state of our knowledge of the fauna of pelecypods of the Kolchugino suite, such compressed specimens as, for example, those figured by Jones under the name Posidonomya subovata, may prove to belong not only to different species, but even to different genera (see p. 74).

Localities and distribution of pelecypods of the Kolchugino suite.

The Ilyinsko-Erunakovsky section of the Kolchugino suite along the Tom River below Stalinsk begins at the village of Bedareva. The pelecypod fauna from this section that was at my disposal was collected from twelve outcrops, of which 9 belong to the Ilyinskaya subsuite and only three to the Erunakovskaya. This section has been studied in detail by Yavorsky (31) and Samylkina (25), and in general outline, according to the data of these authors, it is represented as follows:

Outcrops of the Ilyinskaya subsuite extend from the village of Mitina to the mouth of the Suriakova River. The deposits of this subsuite consist of a frequent alternation of fine-grained gray and yellowish-gray sandstones with calcareous and clayey cement, dark-gray sandy shales, and gray and black clayey shales;

¹) I. V. Lebedev, who is studying a small but interesting collection of pelecypods from the Kolchugino suite of the Osinovsky district, showed me his specimens; of these, some, possessing a taxodont hinge, in outline are apparently indistinguishable from the species concinna and tomiensis and from some figures of “Posidonomya subovata” in Jones.

there are lenses of marls and spherosiderites, thin interbeds of coal and carbonaceous shales. In the sandstones there is often diagonal bedding and ripple marks. The Ilyinskaya subformation contains an abundant, though rather monotonous, fauna of lamellibranchs, crustaceans, and, rarely, fish scales. This fauna (with the exception of fish scales) is in places so abundant that entire beds are composed of it. Usually, however, it is always present in the roof of coal interbeds, composed of clayey shales, in the part nearest to the coal. In the roof composed of sandy shales, fauna is often absent. The beds of black clayey shales contain abundant fauna, predominantly small crustaceans, but they are not devoid of lamellibranchs either. Much more rarely do we find here a fauna of lamellibranchs in beds of sandy shales and, judging from its preservation, there is reason to suppose that it is not in situ (37, 1045).

The Erunakovskaya subformation is composed of the same petrographic varieties as the Ilyinskaya, but in different proportions: the coal beds in the Erunakovskaya subformation possess great thickness; the sandstones likewise form thick beds and are coarser-grained. However, these differences are sharply expressed only in the upper part of the Erunakovskaya subformation, while its lower part shows great lithological similarity to the Ilyinskaya subformation. “There is no sharp boundary between the deposits of the lower, nonproductive part of the Kolchuginskaya series and its upper, productive part” (37, 1048). The pelecypod fauna is confined to the lower part of the Erunakovskaya subformation.

The deposits of the Ilyinskaya subformation form numerous large and small folds, complicated by many disjunctive disturbances of varying amplitude. Because of this, the different horizons of the Ilyinskaya subformation exposed in various parts of the section under consideration cannot at present be stratigraphically correlated. The most complete section of the Ilyinskaya subformation occurs below the mouth of the Uskat River, where a monoclinal sequence 1000 m thick is exposed; the uppermost beds of this section already belong to the Erunakovskaya subformation (37, 1048). The latter is fully developed below the mouth of the Surikovaya River, forming a large gentle syncline, the limbs of which are complicated by minor folding and small disjunctive disturbances; the thickness of this subformation, according to Samylkin, is 2200 m.

Plate C shows the section of the Kolchuginskaya series along the Tom River characterized above. The drawing is a strong schematization of the detailed sections given by Yavorsky and Samylkin, and is included in order to give the most general picture of the occurrence of the deposits from the different horizons of which the fauna described in the present work was collected. Points 1–23 on this section indicate those localities at which the fauna was collected. As can be seen from this section, exposures 1 and 21 are confined to such segments of it as cannot be directly connected with one another, nor with the main section of the Ilyinskaya subformation below the mouth of the Uskat River. As will be seen from the further account, the fauna at these two points is very poor and can give only certain, not entirely definite indications of the stratigraphic position of those horizons to which exposures 1 and 21 correspond.

The greatest interest is naturally presented by the section of the Ilyinskaya subformation below the mouth of the Uskat River already mentioned above. From this section, which is the most complete section of the Ilyinskaya subformation, fauna was obtained from six different beds. These beds (from bottom to top) are designated in Plate A (p. 47) by the letters A, B, C, D, E, F, and the exposures corresponding to these horizons are numbered: 16/17, 15, 13, 12, 11, and 10. The fauna collected in these six horizons makes it possible to establish the vertical distribution of individual species of pe-

List of pelecypods of the Kolchuginskaya Formation

No.	Form name	No. of occurrence, Ilyinsko-Yerunakovsky section: 1	No. of occurrence, Ilyinsko-Yerunakovsky section: 10	No. of occurrence, Ilyinsko-Yerunakovsky section: 11	No. of occurrence, Ilyinsko-Yerunakovsky section: 12	No. of occurrence, Ilyinsko-Yerunakovsky section: 13	No. of occurrence, Ilyinsko-Yerunakovsky section: 15	No. of occurrence, Ilyinsko-Yerunakovsky section: 16/17	No. of occurrence, Ilyinsko-Yerunakovsky section: 21	No. of occurrence, Ilyinsko-Yerunakovsky section: 23	Leninsky mine: roof of the Kamyshinsky seam	Leninsky mine: Kedrovskaya mine
1	Anthracomya supralilipsii n. sp.	–	–	–	–	–	–	–	–	+	–	–
2	Anthracomya tschermyschewi n. sp.	–	–	–	–	–	–	+	–	+	–	–
3	Anthracomya sp., cf. A. orienti Dix et Tru.	–	–	+	–	–	–	–	–	–	–	–
4	Anthracomya trigonalus n. sp.	–	+	–	–	–	–	–	–	–	–	–
5	Anthracomya (?) porrecta n. sp.	–	–	–	–	–	–	+	–	–	–	–
6	Anthracomya obliqua n. sp.	–	–	–	–	–	+	–	–	–	+?	–
7	Anthracomya subparallela n. sp.	–	–	–	–	–	–	–	–	+	–	–
8	Anthracomya similis n. sp.	–	–	–	–	–	–	+	–	+	–	+
9	Anthracomya fedotovi n. sp.	–	–	–	+	–	+	–	–	–	+	–
10	Anthracomya fedotovi, n. var. lata	–	–	–	–	–	–	+	–	–	+	–
11	Anthracomya fedotovi, n. var. producta	–	–	–	–	–	+	–	–	–	+	–
12	Anthracomya tchernesi n. sp.	–	–	–	–	–	–	–	–	–	–	–
13	Anthracomya simplex n. sp.	–	–	+	–	–	–	+	–	–	–	–
14	Anthracomya lata n. sp.	–	–	–	–	–	+	–	–	–	–	–
15	Anthracomya n. sp., cf. A. curta Brown	–	–	–	+	–	+	–	–	–	–	–
16	Anthracomya n. sp.	–	–	–	–	–	+	–	+	–	–	–
17	Palaeanodonta cf. castor Eichw.	–	+	+	–	+?	+	–	+	+	–	–
18	Palaeomutela microdonta n. sp.	–	–	+	–	–	+?	–	–	–	–	–
19	Palaeomutela (?) concinna Jones	–	–	+	+	+?	+?	+	–	+	+	–
20	Palaeomutela (?) tomiensis Rag.	–	–	+?	–	–	+	–	–	–	–	–
21	Palaeomutela (?) nana n. sp.	+	–	–	+	–	–	+	–	+	+	–
22	Posidonomya subovata Jones	–	+?	–	–	–	+	+	–	+	+	–
23	Posidonomya linguloides n. sp.	–	–	–	–	–	–	+	–	–	–	+

Pelecypods in the Ilyinskaya subformation of the given section. From the same schematic section it is evident that only in the lower part of the Erunakovskaya subformation, below the mouth of the Suriekovaya River, was the fauna found in two horizons. These horizons are designated in table A by the letters G and H, and the outcrops corresponding to these horizons have numbers 22 and 23. Let us turn to the consideration of the section of the Ilyinskaya subformation below the mouth of the Uskat River.

The lowest horizon from which fauna was delivered for processing is bed A (outcrop 16/17), situated approximately 200 m from the base of the Ilyinskaya subformation in the given section. In immediate proximity to it, at a distance of 35 m, lies bed B (outcrop 15). The fauna of these two beds will characterize the lower part of the Ilyinskaya subformation, since the next fossiliferous bed C (outcrop 13) is located at a considerable distance from bed B (~200 m) and could characterize faunistically the middle of the Ilyinskaya subformation, if the fauna from this bed were not extremely scanty and in most cases indeterminate. The next three beds with fauna are already situated in the upper part of the Ilyinskaya subformation. The distances between beds C, D, E, F are respectively 190 m, 130 m, and 40 m.

Bed F is thus the highest in the Ilyinskaya subformation, but above it, in the section under consideration, there lies a strata of still considerable thickness (~200 m) in which fossiliferous rocks were not found. And in those very lower beds of the Erunakovskaya subformation which crown the given section and are exposed near the very mouth of the Uskat River, there was found in only one horizon such a scanty and imperfect fauna that its determination proved impossible, and the corresponding horizons therefore are not included in table A.

All the beds of the Ilyinskaya subformation enumerated above are plotted to scale in the table; it also shows two beds (G, H) of the Erunakovskaya subformation in which fauna was found, although topographically these two horizons are considerably removed from the Uskat section of the Ilyinskaya subformation; they are located in outcrops of the Erunakovskaya subformation below the mouth of the Suriekovaya River. The lower of them (bed G) is located at a distance of 180 m from the base of the Erunakovskaya subformation in the indicated area; the distance between horizons G and H is ~500 m; as for the two-kilometer-thick strata of the Erunakovskaya subformation lying above horizon H, from all this strata I have at my disposal not a single pelecypod specimen.

I proceed to the characterization of the fauna of individual outcrops (their location and schematic indications of the conditions under which the fauna was found are taken from the diary of L. A. Stavsky, who collected the fauna).

Outcrop 1 is situated at a distance of 750 m above the mouth of the Patrik River, near the village of Ilyinskoye; the rock containing the fauna is a black carbonaceous clay shale, lying in the roof of a coal seam. The thickness of the carbonaceous-clayey shale bed is about 2 m; the fauna is confined to its lower part and occurs over a thickness of 30 cm from the coal seam.

The fauna from this outcrop is fairly numerous, but poorly preserved, and comparatively few specimens permit exact determination. In this outcrop were found Posidonomya subovata Jones, Palaeomutela microdonta n. sp., Palaeomutela (?) tomiensis Rag., Anthracomya sp., ostracods; plant remains occur (Noeggerathiopsis and fragments of leaves of other plants). Judging by this faunal composition, the deposits to which outcrop 1 belongs probably represent a rather high horizon of the Ilyinskaya subseries.

Outcrop 8 is situated 100 m below the mouth of the Uskat River. This is one of the outcrops of the lower part of the Erunakovo subseries of the Uskat section. The fauna occurs in a meter-thick bed of clay shale that forms the roof of a thirty-centimeter coal seam. The fauna is found in immediate proximity to this coal seam, occurring only over a thickness of 2 cm.

Despite the exceptional interest that the fauna from this outcrop would present, characterizing the transition from the Ilyinskaya suite to the Erunakovo one, I have not even included this horizon among the fauniferous beds shown in Table A; this is explained by the fact that several samples obtained from this outcrop contain only indeterminate fragments of pelecypod shells (belonging to the genera Anthracomya and, possibly, Posidonomya) and small ostracods; together with this fauna, leaves of Noeggerathiopsis occur.

Outcrop 10 is located at a distance of 860 m below the mouth of the Uskat River. A ten-centimeter interbed with fauna and flora is enclosed in a 2 m thick bed of clay shale, at a distance of 20 cm from its footwall. The fauna is fairly numerous, but very poorly preserved; besides small ostracods, in this horizon occur Anthracomya trigonalis n. sp. (one specimen), Anthracomya sp., Posidonomya subovata (?), as well as leaves of Noeggerathiopsis.

Outcrop 11 is located at a distance of 950 m below the mouth of the Uskat River. The fauna was encountered in the lower part of a bed of clay shale; it is similar to the fauna of the preceding outcrop, not numerous, but shows somewhat better preservation. Found here were: Anthracomya cf. wrighti Dix et Tr., Anthracomya tomiensis n. sp., Palaeomutela (?) cf. concinna Jones; ostracods are considerably fewer than in the preceding outcrop.

Outcrop 12 is located at a distance of 1060 m from the mouth of the Uskat River. The conditions of occurrence of the fauna are analogous to the preceding case: in the lower part of a two-meter bed of clay shale, at a distance of 20 cm from its base, there is a ten-centimeter interbed containing fauna and flora. The fauna is very poorly preserved, in most cases represented by shell debris, and moreover it was collected in insufficient quantity. From this horizon it was possible to determine: Palaeomutela (?) tomiensis Rag., Palaeomutela microdonta n. sp., Anthracomya cf. curtata Brown, Anthracomya fedotovi n. sp.; in addition, ostracods are present.

Outcrop 13 is situated at a distance of 160 m from the mouth of the Salairka River. The conditions of occurrence of the fauna are the same as in the preceding cases; the fauna is very poor, badly preserved, and collected in insufficient quantity. Not a single specimen permits exact determination; apparently, there are fragments of Palaeomutela microdonta; leaves of Noeggerathiopsis are present.

Outcrop 15 is located at a distance of 660 m from the mouth of the Salairka River. The fauna is of good preservation and is enclosed in dark bluish-gray dense unfissile argillite with a conchoidal fracture. The bed of this argillite, 15 cm thick, is enclosed between two thin interlayers of brown-gray thin-bedded argillite. The fauna is represented mainly by pelecypods; ostracods occur in smaller numbers. The pelecypod shells are strongly crushed; there are quite many unopened shells; this outcrop, together with outcrops 16–17, yielded the best and most abundant fauna. The most widely distributed here are: Anthracomya obliqua n. sp., Anthr. fedotovi n. sp., Anthr. tschertyschewi n. sp.; also present are: Anthracomya cf. curtata Brown, Anthr. lata n. sp., Anthr. fedotovi n. var. producta, Anthr. n. sp., Posidonomya subovata Jones, Palaeomutela (?) cf. concinna Jones, Palaeomutela (?) tomiensis Rag.; along with well-preserved shells, shell debris occurs in places; some hand specimens contain well-preserved pelecypod shells together with excellent impressions of Tychopteris and Noeggerathiopsis, but in general plant impressions are few.

Outcrops 16–17. These outcrops consist of two fauna-bearing beds, each 5 cm thick, separated by a barren interbed 15 cm thick. The upper bed (16) is lithologically similar to the preceding one. Bed 17 is a fine-sandy variety of dark-gray argillaceous shale. In bed 16 the fauna is comparatively poor; in bed 17 it is abundant and very well preserved; many specimens are entirely undeformed. In these beds the greatest distribution is shown by Posidonomya subovata Jones, whose good, undeformed shells, permitting the establishment of its diagnostic characters, come precisely from this outcrop. In addition, the following have been found here: Anthracomya tschernyschevi n. sp., Anthr. fedotovi n. sp., Anthracomya simplex n. sp., Anthr. porrecta n. sp., Palaeomutela (?) cf. concinna Jones, Pal. (?) tomiensis Rag. Posidonomya linguloides n. sp., and fairly numerous leaves of Noeggerathiopsis.

Outcrop 21 is located 360 m below the mouth of the Markina River. In the bed of argillaceous shale there is a 10-centimeter interbed with fauna and flora. The number of specimens taken from this outcrop is very small. They contain Palaeanodonta cf. castor Eichw., Anthracomya sp., Posidonomya sp.; there are also poor impressions of Noeggerathiopsis and Phyllotheca.

Outcrop 22 is located at a distance of 360 m from the mouth of the Surnekova River. In the argillaceous shale there is a five-centimeter bed with a large number of impressions of Phyllotheca; in the roof of this bed there is a three-centimeter interbed with a sparse and poorly preserved fauna. In the specimens taken from this outcrop only indeterminate fragments of Posidonomya shells and numerous small ostracods are visible.

Outcrop 23 is located at a distance of 1200 m below the mouth of the Surnekova River. It is a two-meter bed of argillaceous shale filled with pelecypod shells. This is the only case in which the fauna is distributed more or less uniformly in so thick a bed; usually the fauna is confined only to thin interbeds a few centimeters or tens of centimeters thick. In this outcrop the fauna occurs in enormous quantity, literally filling the rock, but is rather monotonous and for the most part poorly preserved. However, among several hundred specimens delivered from this outcrop, it was possible to find some which, on the one hand, preserved the hinge and, on the other, preserved the relief of the valves; in species composition the fauna of this outcrop differs rather sharply from the fauna of the Ilyinskaya subformation. In enormous quantities there occur here Anthracomya subparallela n. sp., Anthr. supraphillipsii n. sp., and Palaeomutela microdonta. Along with them occur Anthracomya tschernyschevi n. sp. and Posidonomya subovata Jones, also found in the Ilyinskaya subformation. No change in the composition of the fauna is observed throughout the full two meters of this bed.

The data presented above on the fauna of the individual outcrops make it possible to construct a table showing the distribution of pelecypods in the section of the Kolchugino suite along the Tom River; this table is given on p. 34.

As can be seen from this table, three associations of forms are indicated, characterizing, first, the lower parts of the Ilyinskaya subformation; second, the upper part of this subformation; and third, the lower part of the Erunakovskaya subformation. For the lower part of the Ilyinskaya subformation the following are characteristic: Anthracomya lata, Anthr. obliqua, Anthr. simplex, Anthr. similis, Anthr. porrecta. The upper part of the Ilyinskaya subformation is characterized by the species: Anthr. trigonalis, Anthr. tomiensis, Anthr. cf. wrighti. The lower parts of the Erunakovskaya subformation are characterized by the species Anthr. supraphillipsii and Anthr. subparallela; in addition, Palaeomutela microdonta is widespread here in large numbers, appearing, however, already in the upper parts of the Ilyinskaya subformation. Apparently, for the Ilyinskaya subformation as a whole, Anthr. fedotovi n. sp. and Palaeomutela

tomiensis Rag. Throughout the entire section there occur Anthr. tschernyschewi and Posidonomya subovata.

Thus, the pelecypod fauna makes it possible to subdivide the Kolchugino suite in this section into three horizons. Naturally, the question arises to what extent this subdivision of the Kolchugino suite can be extended to other areas of its development. In connection with this question I consider it necessary to characterize the material on the basis of which Table A was compiled.

First of all I must note that I personally did not have the opportunity to participate in the collection of the fauna and to ascertain that the fauna was collected from all the beds in which it occurs.

Furthermore, already in reviewing the fauna of individual outcrops it was noted that far from all outcrops, and not all beds with fauna, yielded equally abundant and sufficiently well-preserved material. From such outcrops as 13, 8, and 22, such scanty material was collected that it is not possible to form any fairly complete idea of the fauna of these horizons. It is not excluded that with more careful and abundant collecting from these horizons it would be possible to obtain more exhaustive material. For the present, however, some horizons in the collection available to me are represented by such insignificant and imperfect material that it cannot be used for determining the vertical distribution of pelecypods. To this must be added that in a number of outcrops the paleontological material is represented by specimens of extremely poor preservation, permitting only approximate determinations; this also to a certain degree limits the possibility of accurately establishing the stratigraphic position of some species. Finally, the following circumstance must also be taken into account: whereas some species are represented in our collection by an enormous number of specimens, other forms have been established on the basis of only one or two specimens. Among the species occurring in mass development are: Anthr. supraphillipsi, Anthr. tschernyschewi, Anthr. obliqua, Palaeomutela microdonta, Posidonomya subovata, and some others. Conversely, such species as Anthr. porrecta, Anthr. similis, Anthr. trigonalis, Anthr. tomiensis, and some others are represented in our collection by single specimens. It is possible that such rare forms, with more careful collecting of the fauna, may be found not only in those horizons from which they are present in my collection.

In addition to the particular circumstances enumerated above, it is, of course, necessary to take into account also such a most important factor of a general character as the facies nature of the sediments, since the distribution of the fauna in any section may be determined not only by the stratigraphic position of particular horizons, but also by their facies character. It is true that no especially sharp change of fa—

special conditions for the fauna-bearing horizons of the Ilyinskaya and Erunakovo subformations cannot be discerned; in general all these horizons are composed of very fine-grained clayey or carbonaceous-clayey material. Nevertheless, certain fluctuations in the facies character of the sediments composing these horizons are quite evident. On the other hand, in the present section we have unquestionable evidence that the fauna under consideration, at least in some part of it, is very sensitive to facies fluctuations. Evidence for this proposition may be furnished by the fauna from beds A and B of the Ilyinskaya subformation: these beds, occurring in immediate proximity to one another, are composed of rocks that differ somewhat in their properties: bed A, as already noted above, is represented by unstratified dense argillite, whereas bed B is a fine sandy-clayey sediment. And thus, in parallel with this change in lithological composition, we observe in these two beds a considerable difference in the fauna, as is seen from the following table:

	Bed A	Bed B
Anthracomya lata	—	+
Anthracomya obliqua	—	+
Anthracomya tschernyschewi	+	+
Anthracomya fedotovi	+	+
Anthracomya fdotovi var. producta	—	+
Anthracomya simplex	+	—
Anthracomya similis	+	—
Anthracomya porrecta	+	—
Anthracomya cf. curtata	—	+
Anthracomya n. sp.	—	+
Palaeomutela (?) tomiensis	+	+
Posidonomya subovata	+	+
Posidonomya linguoides	+	—

The difference in the fauna of these two beds, which is evident from the given table, can hardly be explained by a difference in the stratigraphic position of these horizons: the distance between them is only 35 m; it is much more natural to explain this difference in the fauna by a difference in the facies character of the corresponding deposits. The example cited shows how essentially necessary it is to take the facies factor into account when compiling the final table of the vertical distribution of pelecypods in the coal-bearing deposits of Kuzbass.

All the considerations set out above compel us, at the present level of our knowledge of the pelecypod fauna of the Kolchugino series, to regard table A as having local significance for the given section and to refrain from extending this scheme to the Kolchugino series as a whole.

For resolving the question, however, of the extent to which the distribution established by us

the vertical distribution of pelecypods is local, and to what extent it is common to the deposits of this suite; it is obviously necessary to carry out analogous work on some other complete section of the Kolchugino suite. When the data obtained from the study of two sections are compared, the probability is that it will be possible to provide a scheme for subdividing the Kolchugino suite on the basis of the pelecypod fauna.

From the Leninskii mine, as already noted above, a very meager fauna was delivered. In the core from the roof of the Kamyshinskii bed the following were identified:

Anthracomya fedotovi n. sp.
      ”     fedotovi n. var. lata
      ”     cf. obliqua n. sp.
      ”     sp.
Posidonomya subovata Jones.
Palaeomutela (?) concinna Jones.
Palaeomutela (?) nanella n. sp.

From the dumps of the Kapitalnaya I mine a very meager fauna was delivered (five specimens), but a distinctive one; precisely here were found three specimens of the original Posidonomya linguloides n. sp. and two specimens of some other species, apparently of the same genus, but because of poor preservation it proved impossible to study this species.

Finally, in the dumps of mine A there were found specimens, not permitting any very precise determination, belonging to some species distinguished from all the other pelecypods of our collection by dense, sharp, irregular concentric wrinkles on the surface of the valves.

Thus, the material delivered from the Leninskii mine is so scanty and fragmentary that it is impossible, on the basis of its study, to draw any stratigraphic conclusions. Nor is it possible to compare it with the fauna of the Il’insko-Erunakovskii section. But one conclusion nevertheless appears obvious: at all three localities of this fauna its composition is different; that is, the various horizons of the Kolchugino suite of the Leninskii district contain different pelecypod faunas, and consequently, with more complete collections, this fauna may provide a basis for the stratigraphic subdivision of the corresponding deposits.

On the age of the deposits of the Kolchugino suite.

As is known, with regard to the age of the Kolchugino suite, the opinions of paleobotanists are more unanimous than with regard to the age of the other suites of the productive series of Kuzbass: in any case, the Permian age of this suite has not elicited objections from any of the paleobotanists who have studied the fossil

the flora of the Kuzbass. No less unanimous, but directly opposite, is the view of the age of the Kolchugino series held by the paleozoölogists who have dealt with the fauna from this series.

Beginning with Amalitsky, who identified in the fauna of this series Posidonomya becheri and Anthracomya carbonaria, and Jones, who described from the deposits of this series a number of Carboniferous anthracomyiids, the Carboniferous age of the deposits of this series has up to now met with no objections in any of the later works on the fauna of the productive measures of the Kuzbass¹. Thus, Stoyanov recognized a Carboniferous age for the deposits of the Kolchugino series. Yanishevsky expressed himself very decisively in the same spirit. In his first works on the age of the deposits of the Kolchugino series, Ragozin spoke rather cautiously, although he also believed that among the fauna of this series there was a whole series of Carboniferous forms. But in his later works this author definitely speaks of the Carboniferous age of the entire productive measures of the Kuzbass, although in these works he no longer cites even a single Carboniferous form.

[The unfoundedness of Ragozin’s conclusions has been analyzed by me in an article published in Problems of Soviet Geology (44)].

Standing apart is Grabau’s opinion, who, together with the paleobotanists, considers these deposits Permian and, in order to reconcile such a determination of their age with the Carboniferous forms indicated from these deposits by Stoyanov, considers it possible to allow the existence in Siberia of these forms at a later time than in Europe, speaking of their possible migration from west to east.

Turning to consideration of the list of Kolchugino pelecypods given on p. 39, for the purpose of resolving the question of the age of the Kolchugino series, we must first of all note the following circumstances.

First, in this list there are no reliable Carboniferous forms, in particular—all those species that were indicated from the Kolchugino series by the above-mentioned authors. This circumstance obliges us to reconsider the question of the age of the fauna (and, consequently, also of the deposits) of the Kolchugino series. Secondly, our list contains exclusively new or previously established, but native, forms; because of this circumstance the fauna described in the present work cannot give a direct answer to the question of the age of the deposits of the Kolchugino series, and this question must be decided on the basis of the totality of direct and indirect indications.

Carboniferous forms are absent in our fauna, but on the other hand there are quite many species close to such forms. Above, on pp. 19–20, an explanation of this phenomenon has already been given; here it will be

Vertical distribution of pelecypods in the Ilyinsko–Erunakovskoe section of the Kolchugino suite

Table A

Name of form	Ilyinskaya sub-suite below the mouth of the Uskat River: 1000 according to Yavorsky. Fauna-bearing beds: A	B	C	D	E	F	Lower part of the Erunakovskaya sub-suite below the Surnekova River. Fauna-bearing beds: G	H
Anthracomya supraphillipsii n. sp.	—	—					—	—
Anthracomya tschernyschewi n. sp.		—					—	—
Anthracomya sp., cf. A. wrighti Dix-et T.					—	—
Anthracomya trigonalis n. sp.		—
Anthracomya porrecta n. sp.		—
Anthracomya obliqua n. sp.		—
Anthracomya subparallela n. sp.							—
Anthracomya similis n. sp.		—
Anthracomya jedlovi n. sp.	—	—		—
Anthracomya jedlovi n. var. producta		—		—
Anthracomya toniensis n. sp.					—
Anthracomya simplex n. sp.		—
Anthracomya lata n. sp.
Anthracomya n. sp., cf. A. curta Brown		—		—
Anthracomya n. sp.		—
Palaeonadonta cf. castor Eichw.
Palaeomutela microdonta n. sp.
Palaeomutela (?) toniensis Rag		—
Posidonomya subovata Jones
Posidonomya tingtoides n. sp.		—

it is sufficient to emphasize that on the basis of these forms we cannot base our conclusions concerning the age of our fauna¹

Among our pelecypods, alongside species close to Carboniferous ones, we have other forms which may be compared with Permian pelecypods. Among them, first of all, the genus Palaeomutela must be noted. This genus has an extraordinarily wide distribution in the Permian deposits of the European part of the Union, Germany, and South Africa, but is absent in the Carboniferous.

Thus, although the species Palaeomutela microdonta, as well as all the other forms provisionally assigned by me to this genus, are endemic and have no close analogues among the pelecypods of other regions and countries, nevertheless the genus Palaeomutela itself, as a whole, is weighty evidence in favor of a younger age for the Kolchugino deposits. Among other forms, Palaeanodonta cf. castor Eichw. may be noted. This form is represented in our collection by a single specimen, which cannot be determined precisely, but its considerable resemblance to the Permian species of Eichwald is nevertheless quite evident.

Thus, among the Kolchugino pelecypod fauna available to us there are no species that could categorically decide the question of the age of this suite. Those same species which can be brought to bear on the resolution of this question give, as we see, contradictory evidence. However, it may be positively asserted that the collection we have studied has shown the following: the elements of the fauna that could speak for a Carboniferous age of the deposits of this suite occupy a subordinate position in this fauna, and their role was greatly exaggerated by previous investigators; while alongside this we have in our fauna considerably more substantial indications of the possibility of assigning it to the Permian period (the Permian genera Palaeomutela and Palaeanodonta).

The latter circumstance acquires all the greater significance because we are compelled to compare our fauna with such Permian faunas as belong to another facies, and consequently it is natural that in the present case we do not find forms that are fully identical. Conversely, those Carboniferous faunas with which we can compare our pelecypod fauna existed under similar physico-geographical conditions, and therefore the presence of many common features in the faunas being compared is natural even if they are of different ages.

The conclusion to which we come on the basis of all the considerations set forth above is as follows: the fauna of the Kolchugino suite is a type of fauna characterizing Permian deposits of the carbonicola facies. And since the fauna of similar deposits has not yet been studied and described in detail, it is natural that

among our pelecypods we see a decisive predominance of new forms. A further refinement of the age of our fauna—namely, determination of the division of the Permian system to which the deposits of the Kolchugino suite belong, on the basis of the materials presently available—is impossible¹.

The solution formulated above to the question of the age of the fauna of the Kolchugino suite is entirely consistent both with the data of paleobotany and with the position of the Kolchugino suite in the general stratigraphic scheme of the Kuzbass deposits, in which our suite is separated by a great thickness from those lower horizons of the Balakhon suite where marine fauna was found by M. E. Yanishevsky—of Upper Carboniferous age. This latter fauna, owing to the terrestrial character of the flora and fauna of the overlying deposits, is the key to determining the age of the productive strata of Kuzbass. Unfortunately, recently doubt has again arisen as to the age of the Lower Balakhon marine fauna (15), but, comparing all the communications available on this question (14, 979; 28, 23; 33; 15, 981), the age of this fauna must be recognized as no older than Upper Carboniferous.

Fauna of the Ilyinsko-Erunakovsky section.

Anthracomya (Anthraconauta) supraphillipsii n. sp.

Pl. I, figs. 1—3. Figs. 4—5.

? 1937. Anthraconauta pseudophillipsii (pars); Fedotov. Lamellibranch mollusks of the coal-bearing deposits, etc., p. 37.

Diagnosis. The shell is developed diagonally, of obliquely oval outline. The hinge margin is straight, comprising half the length of the shell, forming a distinct angle with the posterior margin and passing quite smoothly into the anterior. The posterior margin is straight in the upper and middle part, broadly rounded downward

Fig. 4. Anthracomya supraphillipsii n. sp. Enlarged.

Fig. 5. Anthracomya supraphillipsii n. sp. Enlarged.

and merges quite smoothly with the anterior. The posterior margin is straight in the upper and middle part, broadly rounded downward

and along an arc of large radius passes smoothly into the ventral margin; the upper posterior angle is less than 150°. The ventral margin is convex, without a sinus; from the lower posterior angle it rises steeply to the anterior end; in typical specimens the angle between the ventral and hinge margins is 20–30°. The anterior end of the shell is small, rounded. The greatest height of the shell passes through the posterior end of the hinge margin and amounts to 0.6–0.7 of the shell length.

The beaks are only slightly raised above the hinge margin and are strongly shifted forward (the distance between the beaks and the anterior margin only slightly exceeds 0.1 of the shell length). From the beak to the lower posterior angle there extends a broadly rounded diagonal convexity (keel), from which the surface of the valve descends smoothly forward and backward.

The surface of the valves is covered with sharp concentric wrinkles and with dense fine lines in the intervals between them.

Similarities and differences. From the description given above, and also from the illustrations, it can be seen that this species is extremely close to the European Carboniferous A. phillipsii Will. The table of metric ratios shows that the fluctuations of these ratios are, in general, insignificant and scarcely exceed, on the one hand, the accuracy of measurements of deformed (flattened) specimens, and, on the other, the limits of individual variation. It is necessary, however, to note the following circumstances: in our specimens the beaks are usually shifted somewhat more toward the anterior margin than in the European ones, and are slightly raised above the hinge margin; and the ratio of shell length to diagonal measurement in our specimens is still closer to unity. Although these deviations are very slight, and various variations are observed among European specimens of A. phillipsii, I nevertheless consider it necessary to separate the form described here from Williamson’s species, taking into account these differences as well as the great difference in the stratigraphic position of the two forms: A. phillipsii characterizes the Westphalian stage in Europe and, apparently, is already absent from the Stephanian stage (being replaced there by the closely related A. tenuis Dav. et Trueman, A. jazvorskii B. Tschern. (27, tabl. A). From the species occurring together with A. supraphillipsii it is easily distinguished from A. subparallela by the development of the shell along the diagonal and by the short hinge margin, and from A. tschernyschewi by the straight hinge and straight posterior margins. (However, alongside typical specimens of A. supraphillipsii, there are specimens in which the angle between the direction of the ventral margin and the hinge line is very small; such specimens approach A. subparallela, but nevertheless differ in having a straight posterior margin and a clear angle between it and the hinge line.

[Under the name Anthraconauta pseudophillipsii, D. M. Fedotov (42, 37) described an association of shells which vary greatly in their characters and which, in my opinion, are subject to division into several species. For all their diversity, representatives of Anthraconauta pseudophillipsii possess a posterior margin which “is almost straight, slightly rounded, and forms a very obtuse angle with the hinge margin” (loc. cit., 37). This serves as a distinction from my species, in representatives of which the posterior margin is straight and the posterior dorsal angle is not rounded and is less than 150°. Moreover, Anthraconauta pseudophillipsii occurs in deposits above the Erunakovo subformation and (rarely) in the Ilyinka subformation (42, 39), whereas Anthraconauta supraphillipsii has been found in the lower parts of the Erunakovo subformation, where it occurs in mass quantities; from the Ilyinka subformation there was not a single specimen of this species in my collection.

In addition, among the heterogeneous specimens of Anthraconauta pseudophillipsii, the holotype of this species is not indicated.

All this compels me to refrain from identifying the species Anthraconauta pseudophillipsii Fed. and Anthraconauta supraphillipsii mihi].

Holotype $\dfrac{\mathrm{XXIIIA}}{11}$, paratypes $\dfrac{\mathrm{XXIIIB}}{23}$, $\dfrac{\mathrm{XXIIIB}}{16}$, $\dfrac{\mathrm{XXIIIB}}{3}$, $\dfrac{\mathrm{XXIIIB}}{21a}$, $\dfrac{\mathrm{XXIIIB}}{21b}$.

\(L\)	\(l\)	\(l'\)	\(B^{1)}\)	\(H\)	\(h\)	\(\alpha\)	\(\beta\)	\(\dfrac{l}{L}\)	\(\dfrac{l'}{L}\)	\(\dfrac{H}{L}\)	\(\dfrac{h}{H}\)	\(\dfrac{L}{B1}\)	Specimen no. and locality
23	10	3	24	16.5	11	132°	20°	0.44	0.13	0.72	0.67	0.96	XXIIIB/26, River Tom, outcrop 23.
25	12	2.5	26	17	11.2	138	30	0.48	0.10	0.68	0.66	0.98	XXIIIB/23, River Tom, outcrop 23.
23	12	3	24	13.5	10.5	—	—	0.52	0.13	0.59	0.78	0.96	XXIIIB/16, River Tom, outcrop 23.
26	12.5	—	—	16	12	142	28	0.48	—	0.62	0.75	—	XXIIIB/3, River Tom, outcrop 23.
23	11	2.5	—	12.5	10	—	—	0.48	0.11	0.54	0.80	—	XXIIIB/21a, River Tom, outcrop 23.
—	11	2	—	12	8	—	—	—	—	—	0.67	—	XXIIIB/21b, River Tom, outcrop 23.
15.5	8	2	18	10	7	146	23	0.49	0.12	0.61	0.56	0.92	Anthr. philipsii: Hind (10), pl. XVI, fig. 16.
18	9	3	19.5	12	8.5	145	31	0.50	0.17	0.67	0.71	0.92	Etheridge (6), pl. XII, fig. 7.
25	12.5	3.5	26	13	9	145	28	0.50	0.14	0.52	0.69	0.96	Pruvost (21), pl. VIII, fig. 21.
13	7	—	14	7	4	142	31	0.54	—	0.54	0.57	0.93	Chernyshev (27), table IV, fig. 82.

\(^{1)}\) Measurement of the shell in the diagonal direction.

Distribution: A. supraphillipsii has been delivered in a large number of specimens from the lower part of the Erunakovo subformation, namely from outcrop 23 (bed H).

Anthracomya (Anthraconauta) tschernyschewi n. sp.

Table I, figs. 4—6. Fig. 6.

Diagnosis. The shell is developed in a diagonal direction and has the outline of a regular ellipse with an axial ratio of 1.6 (the long axis is the diagonal dimension of the shell). The hinge margin is moderately long and usually not straight, but slightly convex: its length is somewhat more than half the length of the shell. The posterior margin is regularly rounded, described by an arc of large radius; it joins the hinge margin so smoothly that in typical specimens the point of their junction is discerned with difficulty, the angle formed by them being close to 150°. The ventral margin is likewise smoothly rounded, without any sign of a sinus. The anterior and posterior ends of the shell are smoothly outlined by arcs of approximately equal radius. Owing to the convexity of the posterior margin, the slight convexity of the hinge margin, and the smooth junction of each margin with the adjoining ones, the shell acquires the regular elliptical outline characteristic of this species. The greatest height passes through the posterior end of the hinge margin and amounts to 3/5 of the length of the shell.

Fig. 6. Anthracomya tschernyschewi n. sp. Enlarged.

The umbones are small, slightly raised above the hinge line, and strongly displaced toward the anterior margin. On the specimen with the best-preserved umbo (allotype XV/3a) it has been established that the distance from the umbo to the anterior margin of the shell is close to 1/5 of the shell length, and the length of the part of the hinge margin in front of the umbo is 1/10 of the total length of the hinge margin.

It is impossible, from our specimens, to form a clear idea of the relief of the shell; but, judging from the regularity of the outline of the shell in general and of the ventral margin in particular, it must be assumed that the convexity of the valves in this species is sufficiently even and regular, the keel flatly rounded, and the umbo-ventral depression absent.

The sculpture consists of rather sharp, but not coarse and regular concentric wrinkles and fine, dense striae between them.

Remarks. In addition to the typical specimens of A. tschernyschewi, which possess a noticeably convex hinge margin, there are specimens in our collection in which this margin is almost straight. In such specimens the angle between the hinge and posterior margins is also more clearly expressed. They are connected with the typical specimens by all transitions and in all other respects are fully analogous to them, for which reason I do not find it possible to separate them even as a distinct variety.

Metric relations

\(L\)	\(l\)	\(l''\)	\(l'\)	\(B\)	\(H\)	\(h\)	\(\alpha\)	\(\beta\)	\(\dfrac{l}{L}\)	\(\dfrac{l'}{L}\)	\(\dfrac{H}{L}\)	\(\dfrac{h}{H}\)	\(\dfrac{L}{B}\)	Specimen no. and locality
17	9	7,5	3	17	10	7	152°	14°	0,53	0,18	0,59	0,70	1,00	\(\dfrac{\mathrm{XVI}}{8}\), Tom River, outcrop no. 16/17
17,5	10	9	3	18	10,5	8	142	18	0,57	0,17	0,60	0,76	0,97	\(\dfrac{\mathrm{XV}}{3a}\), Tom River, outcrop no. 15
18,5	10	—	—	—	—	9	—	—	0,53	—	—	—	—	\(\dfrac{\mathrm{XVI}}{1}\), Tom River, outcrop no. 16/17
14	8	—	3,5	14,5	8	5	—	—	0,57	0,15	0,57	0,63	0,97	\(\dfrac{\mathrm{XXIIIB}}{19a}\), Tom River, outcrop no. 23
18	10,5	—	3	—	9,5	6,3	—	—	0,58	0,17	0,53	0,66	—	\(\dfrac{\mathrm{XVII}}{9e}\), Tom River, outcrop no. 16/17
24	12	—	3,8	—	12,8	9,2	142	23	0,50	0,16	0,53	0,74	—	\(\dfrac{\mathrm{XVII}}{10в}\), Tom River, outcrop no. 16/17

Similarities and differences. The regularly elliptical outlines of the shell distinguish A. tschernyschewi from all species described in the literature available to me. Specimens with a weakly convex hinge margin and a noticeable junction of it with the posterior margin approach Anthr. phillipsii Will., from which they differ in the convex posterior margin, the larger angle between the hinge and posterior margins, and the more consistently elliptical outline of the shell. The convex posterior margin in general distinguishes our species from the species of the A. phillipsii group.

Holotype \(\dfrac{\mathrm{XVI}}{8}\) (convex hinge margin, smooth junction of the hinge and posterior margins), allotype \(\dfrac{\mathrm{XV}}{3a}\) (character of the umbo and its position on the hinge margin); paratypes: \(\dfrac{\mathrm{XVI}}{1}\), \(\dfrac{\mathrm{XXIIIB}}{19a}\).

Distribution. A. tschernyschewi belongs to the most widely distributed forms: representatives of this species are common in the lower parts of the Il’inskaya subformation (beds A and B) and have also been found in the lower part of the Erunakovo subformation (bed H).

Antracomya sp., cf. A. wrighti Dix et Tr.

Plate I, fig. 7. Fig. 7.

Comp.: 1931. Anthracomya wrighti: Dix and Trueman: Some non-Marine Lamellibranches etc., p. 183.

Description. The single specimen represents an impression of the right valve. The valve is elongated, with an obliquely oval outline. The straight hinge margin makes up 0.7 of the valve length and is joined smoothly, without a distinct angle, to the posterior margin. The posterior margin is rounded and very smoothly outlines a broad posterior end, passing imperceptibly into the ventral margin. The ventral margin in its middle part is completely straight. The anterior end is small, rounded. The upper dorsal angle is \(130^\circ\), the angle between the hinge and ventral margins is \(30^\circ\). The umbo is located near the anterior margin. The greatest height of the shell passes through the posterior end of the hinge margin and amounts to 0.6 of the valve length. Of the sculpture there are preserved traces of a few wrinkles and fine concentric lines near the margins of the valve.

Fig. 7. Anthracomya sp., cf. A. wrighti Dix et Tr. Enlarged.

Metric ratios

L	l	B	H	\(\alpha\)	\(\beta\)	\(\dfrac{l}{L}\)	\(\dfrac{H}{L}\)	\(\dfrac{L}{B}\)	Specimen no. and locality
11.6	8	12.5	7	\(130^\circ\)	\(30^\circ\)	0.68	0.60	0.92	\(\dfrac{\mathrm{XI}}{7}\), R. Tom’, outcrop 11.

Remarks. The presence of only one specimen, imperfectly preserved, precludes the possibility of making a detailed comparison of it with the species cited in the synonymy; however, the undoubtedly considerable similarity in shell form—in its general outline, in the broadly rounded outline of the posterior margin, in the small size of the angle between the ventral and hinge margins, etc.—is evident. In the present case, as in a number of others, the external similarity of the Kolchugino pelecypods to Carboniferous European species is clearly expressed, being due to the isopic character of the facies and to convergence of faunas.

Plesiotype— $\dfrac{XI}{7}$.

Distribution. The described specimen comes from bed E (top of the Ilyinskaya sub-suite).

Anthracomya (Anthraconauta) trigonalis n. sp.

Table I, fig. 8. Fig. 8.

Diagnosis. Shell developed along the diagonal, subtriangular in outline: the subtriangular figure is formed by a straight hinge margin and by the nearly straight posterior and ventral margins.

The hinge margin is very long, somewhat exceeding $3/5$ of the length of the shell; its junction with the posterior margin is smooth, and apparently the junction with the anterior margin is the same. The anterior end is narrow, rounded; the posterior end is much broader, bounded by a weakly convex posterior margin, forming an indistinct angle of $130^\circ$ with the hinge margin. The lower posterior angle is rounded, but strongly drawn out backward and downward. The ventral margin is almost straight, with a broad and very flat sinus; this margin rises rapidly upward in the direction from the lower posterior angle to the anterior margin, in consequence of which the height of the shell decreases considerably from the posterior end of the hinge margin to the anterior one. The angle formed by the direction of the ventral margin and the hinge line is close to $15^\circ$.

Fig. 8. Anthracomya trigonales n. sp. Enlarged.

The greatest height of the shell passes through the posterior end of the hinge margin and amounts to only one half of the shell length. The umbones are strongly shifted toward the anterior margin and, apparently, project only very slightly above the hinge margin; the distance between the anterior margin and the umbones is $0.15$ of the shell length.

The sculpture consists of numerous regular sharp concentric riblets, the intervals between which are occupied by very fine and dense concentric lines.

Metric ratios

L.	l	l′	B	H	h	α	β	1/L	l′/L	H/L	h/H	L/B	Specimen no. and locality
20	13	3	21	10	6	130°	13°	0.65	0.15	0.50	0.60	0.95	$\dfrac{X}{1a}$, r. Tom, outcrop 11.

Remarks. The diagnosis given above is not complete, since I have at my disposal only one specimen of this species. This specimen is a rather large shell, completely flattened, so that nothing can be said in categorical form about the character of the relief;

judging by the presence and character of the sinus of the ventral margin, it must be supposed that there were corresponding depressions on the valves. Despite the presence of only a single specimen, and one of incomplete preservation, I considered it necessary to describe it as a distinct species, since this specimen possesses very characteristic features and differs sharply from all other pelecypods of the Kolchugino suite.

Similarities and differences. In all characters this species stands closest to the group of Anthr. phillipsii, but differs from all Kolchugino representatives of this group by the presence of a sinus on the ventral margin. From Anthracomya phillipsii it differs, moreover, in its considerably longer hinge margin, a beak less displaced toward the anterior margin, a considerably lower shell, and a non-straight posterior margin. The subtriangular outlines of the shell readily distinguish the species described from Anthracomya tschernyschewi. A specimen described by me under the name Anthracomya sp., cf. A. wrightii, stands closer than the others; this specimen differs in a more convex posterior margin and a considerably larger posterior dorsal angle; furthermore, its ventral margin is straight, without a sinus. The form figured under the name Anthr. phillipsii by Etheridge (6) in fig. 6, pl. XII, approaches our species in its slight development in height and its drawn-out posterior end, but differs in its short hinge margin, large posterior dorsal angle, and straight posterior margin. Comparisons with the remaining representatives of the genus Anthracomya are superfluous. There is, of course, some external similarity in outline with such representatives of Carboniferous Naiadites elongata Hind. as the one figured in fig. 31, pl. XVIII in Hind’s monograph (10).

Holotype — X/1a.

Distribution. The only specimen of this species was found in outcrop 10 (bed D, in the upper part of the Ilyinskaya subsuite).

Anthracomya (Anthraconauta) porrecta n. sp.

Pl. II, fig. 1. Fig. 9.

Diagnosis. Shell strongly elongated lengthwise, with the ventral margin almost parallel to the hinge margin. The hinge margin is straight and constitutes only half the length of the shell. The anterior end, owing to the almost terminal position of the beak, is extremely small; the posterior end, on the contrary, is extremely long, drawn backward and downward, tapering. The posterior margin is straight in its upper and middle part and forms with the hinge margin a rounded angle of 148°. The ventral margin is without a sinus, straight over the greater part of its extent; it becomes convex only in outlining the lower posterior angle and near the anterior end, where it passes quite imperceptibly into the convex anterior margin. The greatest height passes through the posterior end of the hinge margin and constitutes only 0.45 of the shell length.

Fig. 9. Anthracomya porrecta n. sp. Enlarged.

The beaks are situated almost on the anterior margin, set back from the latter by a distance less than 0.1 of the shell length. The beaks are rather broad and blunt, not raised above the hinge line. From the beak to the lower posterior angle there extends a flat-

a rounded elevation, from which the surface of the valve slopes gradually upward and downward.

The sculpture consists of sharp concentric wrinkles, which are coarsest near the anterior margin, and fine lines in the intervals between them.

Metric ratios

L	l	l′	H	h	α	β	1/L	l′/L	H/L	h/H	Specimen no. and locality
22	11	1.5	10	5	148°	16°	0.50	0.07	0.45	0.50	XVII/10d, River Tom’, exposure 16/17

Remarks. To this species there belongs in our collection only one specimen, representing a well-preserved left valve, which possesses extremely characteristic features: an almost marginal position of the beak, a very small anterior end, and an extremely long, drawn-out posterior end, constituting almost half of the valve.

[Anthraconauta porrecta, in the outline of the shell, reveals a considerable similarity to the specimen of Anthracomya tenuis Davies and Truem., figured by the authors of that species in fig. 8, pl. XVI (36); the similarity consists in the strong obliquity of the shell (small angle β), its compression in the dorso-ventral direction, the straight ventral margin, and the strongly drawn-out posterior end; the differences are in the almost terminal position of the beaks in our species, and in the smaller size of the posterior dorsal angle.

In shell outline Anthraconauta porrecta stands in the same relation to Anthraconauta supraphillipsii as Anthraconauta tenuis does to Anthraconauta phillipsii.]

Holotype—XVII/10d.

Distribution—the specimen was found in exposure 16/17.

Anthracomya (Anthraconauta) obliqua n. sp.

Pl. II, figs. 5—6. Figs. 10—11.

Comp. 1901. Anthracomya laevis: Jones. Geol. Magaz., dec. IV, vol. VIII, p. 434, pl. XVI, figs. 6, 7 (non fig. 5).
Comp. 1927. Anthracomya minima: Yanishevsky. Izv. Geol. Kom., vol. 46, no. 9, p. 1018, pl. I, fig. 13.
Non! 1901. Anthracomya minima: Jones, ib., p. 433, pl. XVI, figs. 1—4.
? 1937. Anthraconauta pseudophillipsii (pars): Fedotov. Lamellibranch mollusks, etc., p. 37.

Diagnosis. Shell of medium and small size, obliquely triangular in outline: the hinge margin and the posterior margin form two (often almost equal) sides of the triangle, with an angle between them of about 125°; the third side is the rounded ventral margin.

The hinge margin is straight throughout, rather long—on the average 0.55—0.65 of the shell length; its anterior part (lying in front of the beak) constitutes 0.3 of the entire length of the hinge margin. It joins both the anterior and the posterior margins smoothly, without a break, forming roundings, so that quite precisely

the boundaries of the hinge margin are not discernible. The posterior margin is directed steeply downward; it is broadly rounded, along an arc of large radius it joins the hinge margin and along an arc of smaller radius—the ventral margin, but, nevertheless, the posterior ventral angle is strongly rounded. The posterior part of the shell, in general, is very broad, much broader than the anterior. The ventral margin is smoothly rounded,

Fig. 10. Anthracomya obliqua n. sp.
Enlarged.

Fig. 11. Anthracomya obliqua n. sp.

without any signs of a sinus; from the lower posterior angle forward it rises steeply upward; the angle between the direction of the ventral margin and the hinge line is 25–30°. The anterior margin is rounded.

The greatest height of the shell passes through the posterior end of the hinge margin; it usually reaches 0.7–0.8 of the shell length.

The umbones are slightly raised above the hinge margin and moderately displaced forward: the distance from the anterior margin to the umbones is 0.25–0.30 of the shell length. The convexity of the valves is calm; a keel, as a distinct element of relief, is absent: in its place there is a flatly rounded swelling, behind and in front of which the surface of the valve descends smoothly, without concavities, and whose direction forms an angle of about 50° with the hinge margin.

The sculpture consists of a few coarse wrinkles and dense fine concentric lines.

Metric ratios

L	l	l″	l′	B	H	h	α	β	l/L	l′/L	H/L	h/H	L/B	Specimen no. and locality
7,2	4,2	3	2	8	5,8	4,5	132°	32°	0,58	0,28	0,80	0,77	0,90	XV/7a, Tom’ River, outcrop no. 15
10	6,8	4,8	2,5	10	7	6	—	—	0,68	0,25	0,70	0,85	1,00	XV/5c, ” ” ”
6	4,2	3	2	6	4,5	4	123	27	0,63	0,30	0,75	0,89	1,00	XV/17a, ” ” ”
4	2,2	—	1,2	4	3	2,5	—	—	0,55	0,30	0,75	0,83	1,00	XV/14, ” ” ”
6,5	3,7	2,6	1,7	6,8	4,9	4,8	130	30	0,57	0,26	0,75	0,87	0,95	“Anthr. laevis”: Jones, 12, pl. XVI, fig. 6¹)

¹) Measurements taken from fig. 7 and reduced 3.5 times.

[Remarks. Anthraconauta obliqua shows considerable similarity to the Carboniferous Anthraconauta minima Hind, and initially I was even inclined to regard our form as a variety of the species minima. I consider it necessary to preface the comparison of these two species with a note concerning the synonymy and scope of the species Anthraconauta minima, as well as indications of the presence of this species in the deposits of the Kolchugino series.

The species Anthracomya minima was established by Hind in 1893. Later (in the monograph of 1894–96) Hind identified his species with the species described in 1859 by Ludwig under the name Anodonta minima, and Hind indicated that he had had an opportunity to examine Ludwig’s specimens and that the figures given by this author are poor (10, 117). However, in addition to the figures, Ludwig’s text also contains a definite indication that the shell of Anodonta minima is “am hirteren zugespitze” (16, 36), by which Ludwig’s species differs sharply from all those specimens that were later described and figured by Hind (10, 116), Jones (12, 433), and Pruvost (21, 202) under the name Anthracomya minima Ludwig. In the literature available to me, only Chernyshëv (27, 44) cites Hind as the author of Anthracomya minima, with which one must agree, since Ludwig’s species apparently does not belong to the genus Anthracomya. However, if Hind’s opinion that Modiola carlotta Roemer is a synonym of Anthracomya minima is correct, then, by virtue of priority, Roemer’s name ought to be adopted.

Turning to Hind’s monograph, we first of all establish that this author understood the given species in a very broad sense; this is confirmed especially clearly by the illustrations he provides: for example, the specimen shown in fig. 33, pl. XVI, and having parallel ventral and hinge margins, has nothing in common, apart from size, with the specimen shown beside it (fig. 34), in which the outlines approach an oblique-triangular form. Pruvost assigns to this species specimens of subtriangular outline (see 21, pl. VIII, figs. 17–19). B. I. Chernyshëv defines the outlines of the shell of A. minima quite precisely—“the form of the shell is oblique-triangular” (27, 44). Specimens from the Kuznetsk Basin described by Jones under the name A. minima (12, 433) do not belong to this species, unless one gives it an extremely broad and indefinite scope: one of Jones’s specimens (pl. XVI, figs. 1, 2) stands closest to Anthracomya fedotovi n. sp., the second (ib., figs. 3, 4)—to Anthracomya tomiensis (see pp. 49 and 52). A. minima is cited (without description) by M. E. Yanishëvsky from deposits of the Kolchugino series. In D. M. Fedotov’s opinion, Yanishëvsky’s specimens undoubtedly belong to the species Anthraconauta pseudophillipsii, just as, indeed, do Jones’s specimens described by the latter under the name Anthracomya minima (42, 38). I cannot agree that Jones’s and Yanishëvsky’s specimens can belong to one species; moreover, the specimen figured by Jones (12) in figs. 1, 2, pl. XVI, has nothing in common with representatives of the Anthr. phillipsii group, i.e., it does not even belong to the genus Anthraconauta Pruvost.

Two specimens (museum No. 14) with the label Anthracomya minima in the collection of M. E. Yanishëvsky apparently belong to the species A. obliqua; one of them (figured in fig. 13, pl. 1—see synonymy) is considerably damaged, the other is not fully prepared and is partly hidden in the rock, which is why I cannot state their specific attribution with complete certainty. Among the specimens in the collection of D. M. Fedotov bearing the label Anthraconauta pseudophillipsii, I did not find examples identical with the species Anthraconauta obliqua and with the above-mentioned specimen of M. E. Yanishëvsky.]

Similarities and differences. From Anthraconauta minima our form differs in the absence of a sinus on the ventral margin and, consequently, in the absence of an umbo-ventral depression; in general, in our variety the shell in the direction from the middle of the ventral margin toward the apex of the upper posterior angle is considerably broader than in A. minima Hind. This latter circumstance also distinguishes our specimens from the specimen of A. minima that is figured by Pruvost (21) in fig. 17, pl. VIII, and which, unlike typical specimens, does not possess a sinus on the ventral margin.

Obvious similarity to our specimens is shown by the specimen from the Upper Tersey River figured by Jones (see synonymy) under the name Anthraco-

mya laevis Daws. In the text, after giving a brief characterization of this specimen, Jones very cautiously expressed himself regarding its belonging to Dawson’s species: “this may probably belong to Anthracomya laevis Dawson” (12, 434). From A. laevis, as well as from the closely related but not identical Anthr. scotica Eth. (see 6, 244, pl. XII, fig. 8), Jones’s specimen (as well as our specimens) differs in the lesser development of the shell in height, the more rounded posterior margin, and the beaks situated farther from the anterior margin, as well as in the subtriangular outline of the shell; apparently, Jones’s specimen is identical with ours.

The Kuznetsk specimens mentioned by Yanishevsky (see the synonymy) under the name A. minima also, apparently, belong to A. obliqua; the absence of a description and the not entirely clear figure do not allow me to express myself more definitely on this question.

In general outline, the species Anthracomya obstipa Ludw. from the Permo-Carboniferous deposits of the Urals (18, 22) approaches our specimens; the distinguishing features of Ludwig’s species are: a more developed and often sharper anterior end, a distinctly expressed posterior dorsal angle, beaks situated closer to the center of the hinge margin, and a strong downward deflection of the hinge margin in front of the beak.

It is not without interest to note that certain metric ratios in the shell of A. obliqua almost completely coincide with those in Anthracomya fedotovi (see p. 63), although the differences in the outlines of the shell in these species are obvious.

Holotype — XV/5c; paratypes — XI/17a, XV/7a, XV/14.

Distribution: A. obliqua has been obtained in a large number of specimens from outcrop 15 (bed B in the lower part of the Ilyinskaya subseries).

Anthracomya subparallela n. sp.

Plate II, figs. 2–4. Figs. 12–13.

Diagnosis. Shell developed lengthwise, weakly widening posteriorly, with a very acute angle between the direction of the ventral margin and the hinge margin. The latter is straight, extremely long, amounting to \(4/5\) of the length of the shell; with the anterior and posterior margins it joins smoothly, without distinct angles. The anterior end is short, rounded, narrower than the posterior; the curve outlining it passes quite smoothly into the ventral margin. The ventral margin is weakly convex, straight in the middle part, without a sinus; its lowest point lies opposite the posterior end of the hinge margin—from this point the ventral margin rises slowly forward, while posteriorly, forming a broadly rounded lower posterior angle, it passes into the posterior margin. This latter is weakly convex, sometimes straightened in its middle part; the angle formed by the direction of the posterior margin and the hinge line is relatively small: on average 120–130°, but sometimes decreases to 105°. The greatest—

Fig. 12. Anthracomya subparallela n. sp. Enlarged.

Fig. 13. Anthracomya subparallela n. sp. Enlarged.

the greatest height of the shell passes through the posterior end of the hinge margin and is equal to half the length of the shell.

The beaks are strongly shifted toward the anterior margin, broad, blunt, slightly raised above the hinge margin; the distance from the beaks to the anterior margin is 0.15 of the shell length. The valves are markedly convex. The greatest convexity, in the form of a broadly rounded keel, runs from the beak to the lower posterior angle; from this line of greatest convexity the surface of the valve descends smoothly toward the ventral and hinge margins, forming no depressions either behind or in front of the keel.

The sculpture consists of rather sharp, but not coarse, concentric wrinkles and fine lines.

Metric ratios

L	l	l′	H	h	α	β	l/L	l′/L	H/L	h/H	Specimen no. and locality
13	11	2	7	4.5	105°	14°	0.85	0.15	0.54	0.64	XXIIIA/22, r. Tom, exposure no. 23
21	16	3	10	7.5	120	—	0.80	0.14	0.48	0.75	XXIIIA/36, ” ” ”
18	14	2.5	10	7	130	12	0.78	0.14	0.55	0.70	XXIIIA/23a, ” ” ”

Similarities and differences. This species is well characterized by the following combination of characters: a very long hinge margin, a small posterior upper angle, the length twice exceeding the height, and the angle between the ventral and hinge margins very acute. From all other species of the Kolchugino suite, Anthr. subparallela is easily distinguished by a simple comparison of the metric ratios of the shell elements. Closest to it is Anthracomya elongata Tschern., differing in its shorter hinge margin, straight posterior margin, and blunter posterior dorsal angle. Some resemblance is observed with representatives of the Carboniferous Anthracomya modiolaris Sow. and Anthr. williamsoni Brown, which do not possess a sinus on the ventral margin; but in these species the anterior end of the shell is narrowed and drawn out, which readily distinguishes them from our species.

Holotype XXIIIA/23a; paratypes XXIIIA/36; XXIIIA/22a.

Distribution. Together with Anthr. supraphillipsi this species is widely distributed in the lower part of the Erunakovskaya subsuite (bed H).

Anthracomya similis n. sp.

Plate II, fig. 8. Fig. 14.

Diagnosis. Shell strongly developed in length, with a very acute angle between the hinge and ventral margins. The hinge margin is straight, constituting 0.5–0.6 of the shell length and forming with the posterior margin a very rounded angle of 140°. The posterior end is long, outlined by a curve, weakly convex in the upper part, tapering backward and downward, but with a rounded lower posterior angle. The ventral margin is weakly convex, almost straight in the middle part, without a sinus, smoothly joining with the pos—

…posterior and anterior margins. The anterior end is very short, rounded. The greatest height passes through the posterior end of the hinge margin and amounts to 0.5 of the shell length.

The umbones are strongly displaced toward the anterior margin, fairly broad, slightly raised above the hinge line; they are set back from the anterior margin by a distance of 0.12 of the shell length. From the umbo to the lower posterior angle there runs a rounded diagonal elevation (keel), clearly bounded by a steep slope in the posterior-upper direction and smoothly descending toward the ventral margin. The sculpture consists of sharp concentric wrinkles and fine lines between them.

Fig. 14. Anthracomya similis n. sp. Enlarged.

Metric ratios

L	l	l′	H	h	α	β	l/L	l′/L	H/L	h/H	Specimen no. and locality
17	9	2	8	5	140°	20°	0.53	0.12	0.47	0.62	XVII/10e, R. Tom, exposure no. 17
17	11	2	9.5	6.5	—	—	0.65	0.12	0.56	0.68	XXIIIA/7a, R. Tom, exposure no. 23

Remarks. This species, in a number of characters, resembles certain other species of the genus Anthracomya from the Kolchugino series; however, it differs from each of them in a series of characters. Therefore I am unable to unite it with any of the species known to me and am compelled to describe it under a new name.

Similarities and differences. Anthracomya similis shows great similarity to Anthr. subparallela, but differs from it in the following characters: the hinge margin is considerably shorter, the upper posterior angle is more obtuse, the posterior end is longer and tapering, and the shell also narrows more toward the anterior end. The specimen described below under the name Palaeantodonta cf. castor Eichw. differs in its long, narrowed anterior end, much longer hinge margin, umbo more remote from the anterior margin, and smaller and more distinct posterior dorsal angle.

Holotype — XVII/10e.

Distribution. One specimen comes from exposure 17 (the lowermost of the fossiliferous beds of the Ilyinskaya subseries), the second—from exposure 23.

Anthracomya fedotovi n. sp.

Compare 1901. Antracomya minima: Jones. Geol. Mag., dec. IV, vol. VIII, p. 433, pl. XVI, figs. 1, 2 (non figs. 3, 4).

Table II, figs. 9, 10. Figs. 15–16.

Diagnosis. Shell elongated, oval in outline. The hinge margin is straight, constituting 0.65 of the shell length.

The posterior margin is broadly rounded, joining smoothly with the hinge margin, without forming a distinct angle; the angle between the direction of the posterior margin and the hinge margin is about 130–140°. The posterior lower angle is broadly rounded. The ventral margin is convex, almost parallel to the hinge margin; its lowest point lies approximately opposite the middle of the distance between the beak and the posterior end of the hinge margin. From this point the ventral margin rises very slowly toward the posterior margin and somewhat more rapidly toward the anterior. The ventral margin has no signs of a sinus. The anterior margin is smoothly rounded. The anterior end, in general, is broad, only slightly narrower than the posterior. The greatest height of the shell passes approximately through the middle of the length of the hinge margin.

Fig. 15. Anthracomya fedotovi n. sp. Enlarged.

Fig. 16. Anthracomya fedotovi n. sp. Enlarged.

The beaks are small, only slightly raised above the hinge line, displaced toward the anterior end: they are situated at a distance of \(1/4\) of the shell length from the anterior margin. The convexity of the valves is uniform; there is no more or less distinctly expressed keel or depression in front of it.

Metric ratios

L	l	l″	l′	B	H	h	α	β	l/L	l′/L	H/L	h/H	L/B	No. of specimen and locality
8	5,2	4	2	8,2	5,5	4,8	130°	—	0,65	0,25	0,69	0,87	0,97	XV/5a, r. Tom, outcrop No. 15
12	7	5,8	3	12	7	6	140	15°	0,58	0,25	0,58	0,86	0,96	XV/13, ” ” ”
11	7	5	2,2	11	6,5	5	130	—	0,64	0,20	0,59	0,77	1,00	XV/6, ” ” ”
10,5	7	5,2	2,6	11	6,8	5,8	130	16	0,67	0,25	0,65	0,87	0,95	XVII/1a, r. Tom, outcrop No. 17
10	6,4	—	2,1	10	5,4	4,3	143	15	0,64	0,21	0,54	0,80	1,00	“Anthr. minima”: Jones, 12, pl. XVI, fig. 1¹)

¹) Measurements taken from fig. 2 and reduced 2.8 times.

Sculpture—few sharp wrinkles and thin concentric lines.

Similarities and differences. As is evident from the description of our species given above, it shows considerable similarity to Anthracomya ovata B. Tschern. from the Donets Basin. Anthracomya fedotovi is somewhat more developed in height: \(\frac{H}{L}\) in our species varies within the limits 0.58–0.69, whereas in Anthracomya ovata this ratio is equal to 0.5. In addition, Anthracomya ovata differs in the greater convexity of the valves, in the incipient umbo-ventral depression, and in the different outline of the posterior end of the shell: whereas in Anthracomya fedotovi the posterior end is completely rounded and similar to the anterior one, in Anthracomya ovata there is a substantial difference in the outlines of the posterior and anterior ends, namely—the posterior margin is slightly truncated and forms noticeable, though rounded, angles with the ventral and hinge margins.

The closely related Anthracomya iakowlewi B. Tschern. differs by an even smaller ratio \(\frac{H}{L}\) (about 0.4), by a somewhat longer hinge margin (ratio \(\frac{l}{L} = 0.7\)), by a more distinct and less obtuse (120°) upper posterior angle, and by a less rounded posterior end. Anthracomya subcentralis Salt. differs in its straight posterior margin and the position of the umbones. Anthracomya tschermyschewi n. sp. differs in a more regular elliptical outline, an even less distinct and considerably more obtuse posterior dorsal angle, a broader anterior end, a shorter and, moreover, weakly convex hinge margin, and a greater displacement of the umbones toward the anterior margin.

In 1901 Jones (see synonymy) described two specimens from the deposits of the Kolchugino suite of the Upper Ters under the name Anthracomya minima Ludwig, of which one, judging from figures 1 and 2 on pl. XVI, is very close to A. fedotovi and differs sharply from Anthr. minima. If one does not take into account the somewhat more obtuse (143°) upper posterior angle, neither the figures nor the brief description (12, 43) make it possible to indicate any differences of this specimen from our specimens.

Holotype—XVI 1/1a; paratypes: XV/6; XV/13; XV/5a.

Distribution: In the Ilyinsko-Erunakovsky section this species belongs to the most common in the lower beds (A and B) of the Ilyinskaya subsuite. It is also encountered in the Leninsky mine.

Anthracomya fedotovi n. var. producta.

Pl. III, fig. 2.

I provisionally give this name to forms that have much in common with typical Anthr. fedotovi, but are not identical with it. The differences reduce to the following: the shell is more elongated in length (the height amounts to only 0.5 of the length); the hinge margin is shorter (a little more than 0.5 of the shell length); the posterior dorsal angle is somewhat more distinct, although it still cannot be called pronounced; the surface of the valve in the postero-upper part descends more sharply, as a result of which, at least on one side, the keel is expressed in higher relief; angle \(\beta\) is smaller.

The remaining characters are common; the most important of them are: a convex ventral margin without a sinus, almost parallel to the hinge margin; the distance from the umbo to the anterior margin is \(1/5\) of the shell length; a rounded posterior margin; oval outlines of the shell.

The difference in outline between typical Anthr. fedotovi and the variety producta stands out clearly upon direct comparison of specimens: schematically, one may assume that the outlines of the shell of the variety producta are obtained by compression in the dorsoventral direction of the typical form.

Taking into account other differences (among those noted above) between these forms, it might perhaps have been more correct to separate the specimens described into an independent species.

Metric ratios:

L	l	l″	l′	b	H	h	l / L	l′ / L	H / L	h / H	L / b	Specimen no. and locality
10	5.5	4	2.2	10	5	4.5	0.55	5.22	0.50	0.90	1.00	XV/56, River Tom, outcrop No. 15.

Holotype — XV/56

Distribution. This variety was found together with the typical form in bed B.

Anthracomya tomiensis n. sp.

Plate III, fig. 3. Fig. 17.

Comp. 1901. Anthracomya minima: Jones. Geol. Mag., dec. IV, vol. VIII, p. 433, pl. XVI, figs. 3,4 (non figs. 1, 2).

Diagnosis. The shell is elongated. Above, it is bounded by a long straight hinge margin, forming a distinct angle of 125° with the posterior margin. In front of the umbo the hinge margin remains horizontal for a very short distance, and then gradually bends downward, imperceptibly passing into the anterior margin. The length of the hinge margin amounts to 0.7 of the shell length. The posterior margin as a whole is weakly convex, but in its upper part almost straight. The ventral margin is convex, in the posterior part almost parallel to the hinge margin. The anterior part of the ventral margin rises rather rapidly upward, imperceptibly passing into a regularly rounded anterior margin. The anterior end is rather broad, but considerably narrower than the posterior end.

Fig. 17. Anthracomya tomiensis n. sp. Enlarged.

The greatest height of the shell, amounting to 0.6 of its length, passes through the middle of the hinge margin and decreases barely perceptibly backward, but rather rapidly forward.

The umbo is strongly displaced forward, being located from the anterior margin at a distance of 1/5 of the shell length. The relief of the valves has not been preserved.

The sculpture consists of sharp concentric wrinkles and fine lines.

Metric ratios

L	l	l″	l′	B	H	h	α	β	l/L	l′/L	H/L	h/H	L/B	Specimen no. and locality
15,5	11	8,5	3	15,5	9	7	125°	17°	0,71	0,19	0,58	0,78	1,00	II/4a, R. Tom, exposure no. 11
13,5	9,2	7	2,7	13,5	8	7	125	15	0,68	0,20	0,59	0,87	1,00	“Anthr. minima”: Jones, 12, pl. XVI, fig. 3

Remarks. The new species Anthr. tomiensis does not possess any striking feature that distinguishes it from closely related species. But, resembling in some of its characters a whole series of species known to me, Anthr. tomiensis, in the aggregate of these characters, cannot be identified with any one of them; for this reason it proved necessary to distinguish it as an independent unit.

Similarities and differences. The broad, not drawn-out anterior end and the absence of a sinus on the ventral margin distinguish our species from a large number of European species with which Anthr. tomiensis might have been compared on other characters (Anthr. modioliaris, Anthr. williamsoni, Anthr. smolaninowskensis, etc.). Anthr. subcentralis Salt. differs sharply in having umbones set closer to the middle of the hinge margin. The Anthr. phillipsii group differs in the oblique outline of the shell, the short hinge margin, the large posterior dorsal angle, and the umbones situated closer to the anterior margin. The Anthr. minima Hind group differs sharply in the subtriangular outline of the shell. Closer to the others stand the Stephanian Anthr. ovata B. Tschern. and Anthr. iakovlevi B. Tschrn., possessing similar outlines and orientation of the shell. Anthr. ovata differs in the absence of a clear posterior dorsal angle, in the strongly rounded posterior margin, and in the more drawn-out lower posterior angle. Anthr. iakovlevi differs in the lesser height of the shell

\[ \left(\frac{H}{L}=0,4\right) \]

and in the somewhat more drawn-out and acute posterior ventral angle; this species is the closest to Anthr. tomiensis, and especially such representatives of it as the one figured by B. I. Chernyshev (27) in fig. 72, pl. IV, whereas fig. 71 on the same plate shows already noticeably greater deviations from our species.

In our collection there is one species, namely Anthr. simplex, which shows complete similarity to A. tomiensis in most characters, but differs in umbones considerably removed from the anterior margin and in a rounded posterior dorsal angle. Since, moreover, these two species occur in different horizons, I did not consider it possible to unite them under one name.

The specimen from the Upper Ters, figured as Anthr. minima in figs. 3–4 of pl. XVI by Jones (12), is apparently identical with our species; the only difference is that in Jones’s specimen the posterior dorsal angle is larger by 10°, in connection with which the posterior end is narrower and sharper. But in this case, as in other cases of comparing our specimens with Jones’s drawings, it must be borne in mind that in rendering details these drawings, in general good, are not accurate (compare, for example, the outlines of the posterior margin in figs. 1 and 2 and in figs. 3 and 4 of pl. XVI). Therefore in all cases I refrain from definitively identifying my specimens with Jones’s specimens, at least until I have specimens from the very same localities from which they were described by Jones.

Holotype—

\[ \frac{XI}{4} \]

Distribution. A. tomiensis forms part of that small collection which was obtained from the upper beds of the Ilyinskaya subformation (bed F).

Anthracomya simplex n. sp.

Table III, figs. 4, 5. Fig. 18.

Diagnosis. The shell is elongated in length. The hinge margin is straight and long, constituting about \(3/4\) of the shell length; anterior to the umbones it lies at the same level as posterior to the umbones, and with the anterior margin forms an obtuse angle with a strongly rounded apex; the part of the hinge margin lying posterior to the umbones is 2.5 times greater than its anterior part. The posterior margin is almost straight in its middle part, rounding where it joins the hinge and ventral margins; the angle between the hinge margin and the direction of the posterior margin is less than \(115^\circ\). The ventral margin is smoothly rounded; its middle point is at the same time the lowest, and from it the ventral margin rises both forward and backward: forward—rapidly and strongly, joining the anterior margin in a completely smooth arc; backward—slowly and slightly; the lower posterior angle is rounded, its magnitude about \(60\text{–}70^\circ\). The ventral margin is not parallel to the hinge margin, but the angle between the latter and the tangent to the ventral margin in its middle part is very acute, about \(15^\circ\). The anterior end is rather broad, but considerably narrower than the posterior; it is outlined by a regular arc.

Fig. 18. Anthracomya simplex n. sp. Enlarged.

The greatest height of the valves passes approximately through the middle of the shell length and decreases backward (to the end of the hinge margin) slowly, while forward the height of the valves diminishes rapidly; the greatest height of the valves equals \(2/3\text{–}3/4\) of the shell length.

The umbones are small, sharp, noticeably projecting above the hinge margin; they are situated at a distance of one third of the shell length from the anterior margin. There is no keel as a distinct element of the relief of the valve; the surface of the valve rises slowly and quite regularly from the anterior and lower margins to the line connecting the umbo and the lower posterior angle, behind and above which the surface of the valve descends more sharply. The absolute convexity of our specimens is not great, but this depends to a certain extent on the fact that the valves are somewhat compressed.

Metric ratios

L	l	l''	l'	B	H	h	α	β	1/L	1'/L	H/L	h/H	L/B	Specimen no. and locality
15,5	11	9	4,5	16	10	8,5	112°	15°	0,71	0,28	0,65	0,85	0,97	\(\dfrac{\mathrm{XVII}}{4a}\), Tom River, outcrop No. 17
8	6	4	2,8	9	6	5	112	—	0,75	0,35	0,75	0,83	0,89	\(\dfrac{\mathrm{XVII}}{4б}\), same, same, same

The sculpture consists of a few sharp wrinkles and fine concentric lines.

Similarities and differences. In a number of characters our specimens show considerable similarity to the species Anthracomya subcentralis Salt., especially to specimens like the one figured by Hind’a (10) in Fig. 20, Pl. XIX, and which, according to Hind’a’s remark, is typical. The similarity consists in the character and position of the umbones, the length of the hinge margin, the size of the posterior dorsal angle, the character of the posterior margin, the absence of a sinus on the ventral margin, and the character of the relief of the valves; i.e., in a number of important characters there is great similarity between our specimens and Salter’s species. However, alongside this there are also differences: in our specimens the lower posterior angle is more acute, and the shell, in relation to its length, has greater height. The most substantial difference is as follows: in Salter’s species the anterior end of the shell is more developed than in our specimens; it is almost as wide as the posterior one, and the height of the shell in the region of the umbo is equal to the height of the shell in the region of the posterior end of the hinge margin, i.e. the height of the shell remains the same throughout the entire extent from the posterior end of the hinge margin to the umbo. In our specimens, however, the height of the shell rapidly decreases toward the anterior margin and in the region of the umbo is already only \(4/5\) of the greatest height. Otherwise this difference may be formulated thus: in subcentralis the ventral margin is less convex and rises very slowly toward the anterior margin; in our specimens the ventral margin is generally somewhat more convex and rises comparatively rapidly toward the anterior end. This accounts for the noticeable difference in the outline of the shell as a whole.

The closest species is the Anthr. tomiensis described above, distinguished by an unrounded posterior dorsal angle and a different position of the umbones: in Anthr. tomiensis the latter are removed from the anterior margin by a distance of only \(1/5\) of the shell length, whereas in A. simplex this distance, on average, is equal to \(1/3\) of the shell length.

Holotype—XVII/4a; paratypes XVII/4b, XVII/2a, XVII/5a.

Remarks. In the rock blocks, together with whole valves of A. simplex, there occur impressions of fragments of pelecypod shells and impressions of well-preserved leaves of Noeggerathiopsis.

Distribution. A. simplex is distributed in the lowest horizons of the Ilyinskaya subformation (bed A); in the upper part of this subformation an extremely close, but not identical, form has been found—A. tomiensis.

Anthracomya lata n. sp.

Pl. III, figs. 5, 7. Fig. 19.

Diagnosis. The shell is weakly developed lengthwise, of suboval outline. The hinge margin is straight, long (\(3/5\) of the shell length); with the anterior and posterior margins it joins smoothly, without forming distinct angles. The anterior, ventral, and posterior margins are convex, outlined by a smooth curve; the anterior end is broad, though narrower than the posterior; the posterior dorsal angle is small—about \(110^\circ\). The direction of the middle part of the posterior margin is almost perpendicular to the hinge margin; this middle, almost straight part of the posterior margin gives the outline of the shell a very characteristic feature: the shell appears as if truncated, cut off at the posterior margin. The umbo is acute, slightly raised above the hinge line and

Fig. 19. Anthracomya lata n. sp. Enlarged.

is set back from the anterior margin at a distance of \(1/5\)—\(1/4\) of the shell length. The shell is very high; the greatest height, reaching \(3/4\) of the shell length, passes through the posterior end of the hinge margin.

The sculpture consists of sharp concentric wrinkles and dense fine lines.

Metric ratios:

L	l	l′	b	H	h	\(\alpha\)	\(\beta\)	\(\frac{l}{L}\)	\(\frac{l′}{L}\)	\(\frac{H}{L}\)	\(\frac{h}{H}\)	\(\frac{L}{b}\)	No. of specimen and locality
13	9.0	2.5	13.8	10	7.5	110°	26°	0.70	0.19	0.77	0.75	0.94	\(\frac{\mathrm{XV}}{18}\), r. Tom, outcrop No. 15.
6.5	4.8	1.2	—	5.2	4.8	—	—	0.74	0.18	0.80	0.92	—	\(\frac{\mathrm{XV}}{7\mathrm{v}}\), ” ” ”
11	7.5	3	—	8	6.2	—	—	0.68	0.27	0.73	0.78	—	\(\frac{\mathrm{XV}}{7\mathrm{d}}\), ” ” ”

Remarks. This species displays such significant peculiarities that it is difficult even to compare it with any of the other species. Unfortunately, all the specimens belonging to this species are crushed valves, which do not give a clear idea of the relief; but judging by the smoothness of the curve outlining the shell (with the exception of the dorsal side), it must be assumed that the valve was regularly convex, without a sharp keel and without a depression in front of it.

Similarities and differences. The most important distinguishing features of this species are the regularly rounded outlines of the ventral and anterior margins, the truncated posterior end, and the very strong development of the shell in height. The last character distinguishes this species from all the other pelecypods of the Kolchugino suite. By this character our species could apparently be compared only with the Carboniferous Anthr. laevis Daws. and A. scotica Ether., and with the Permian A. modiomorphoides Gr., but these species have entirely different outlines (see 3, pl. XIII, fig. c; 6, pl. XII, fig. 8 and 9, p. 485).

Holotype—\(\frac{\mathrm{XV}}{18}\), paratypes—\(\frac{\mathrm{XV}}{7\mathrm{v}}\); \(\frac{\mathrm{XV}}{7\mathrm{d}}\), \(\frac{\mathrm{XV}}{3\mathrm{g}}\)

Distribution. All specimens come from bed B (in the lower parts of the Ilyinskaya subsuite).

Anthracomya n. sp., cf. A. curtata Brown.

Pl. III, fig. 8.

I have three specimens (two left and one right valve), which cannot be assigned to any species of the genus Anthracomya, either among those found in the Kolchugino suite or among those described in the literature available to me. All these specimens are damaged, and I am unable to give any sufficiently complete diagnosis of this new species; therefore I refrain from assigning it a name. A feature distinguishing this species from the other Kolchugino pelecypods is—

... with the general development of the shell in length, a strong expansion of it toward the rear is observed: the posterior half of the shell is much wider than the anterior—of such shells some authors say: “the hinge margin rises considerably backward.” Measurements of one specimen (which could not be made quite accurately, owing to the imperfect preservation of this specimen) gave the following results: the hinge margin is 0.73 of the length of the shell; the umbones lie at a distance of 1/5 of the shell length from the anterior margin; the height of the shell is equal to 3/5 of its length; the upper posterior angle is small—approximately 100–120 degrees.

The posterior end is broadly rounded; the ventral margin is regular and markedly convex, without a sinus; the anterior end is short, rounded. The umbones are small, slightly raised above the hinge line. The sculpture consists of sharp wrinkles and fine lines between them.

Dimensions—15 mm in length, 9 mm in width.

In their general outlines, in particular in the convex ventral margin, the described valves very much resemble Anthr. curtata Brown. (see 10, pl. XIV, fig. 9). The distinction of Brown’s species is the long, pointed anterior end, whereas in our specimens this end is broad and short. This, at first glance insignificant, difference is in fact very substantial: a sharp and long anterior end is characteristic of an entire group of species of anthracomyiids, both European and Asiatic, but the anthracomyiids of the Kolchugino suite, as a general rule, do not possess this character.

Of the specimens described, two \(\left(\dfrac{\mathrm{XV}}{17\ \mathrm{б}}\ \text{and}\ \dfrac{\mathrm{XV}}{3\ \mathrm{б}}\right)\) come from bed B, and one \(\left(\dfrac{\mathrm{XII}}{4\ \mathrm{а}}\right)\) from bed D, i.e. they were found in the lower and in the upper half of the Ilyinskaya subsuite.

Anthracomya n. sp.

Table IV, fig. 1.

One incomplete specimen \(\left(\dfrac{\mathrm{XV}}{5\ \mathrm{г}}\right)\), representing a left valve and coming from bed B, undoubtedly belongs to a certain new species which, unfortunately, cannot be fully characterized because of the insufficiency of the material. Characteristic is the cuneiform shape of the shell of this species, due to the fact that the shell, widening backward and narrowing forward, is bounded above and below by perfectly straight hinge and ventral margins, forming an angle of 28°. The incomplete preservation of the specimen does not permit the necessary measurements to be made; its length is not less than 14 mm, height about 9 mm, and the length of the hinge margin is the same; the umbo is strongly shifted toward the anterior margin and scarcely rises above the line of the latter. The outlines of the anterior and posterior margins have not been preserved. The sculpture is ordinary: coarse wrinkles and fine growth lines.

Palaeanadonta cf. castor Eichw.

Table III, fig. 9. Fig. 20.

Comp. 1860. Unio castor: Eichwald. Lethaea Rossica, vol. I, p. 1003, pl. 39, fig. 20.
1888. Anthracosia castor: Krotov. Trans. Geol. Comm., vol. VI, p. 490, pl. II, fig. 29.
1892. Naiadites castor: Amalitskii. Materials toward the knowledge of the fauna of the Permian system of Russia. I, p. 119, pl. IV, figs. 40—43.
1894. Nayadites castor: Nechaev. Fauna of the Permian deposits etc., p. 282, pl. IX, figs. 1—5, 10.

Diagnosis. “Shell elongate, oval, almost rhombic, moderately convex; middle forms parallelogram-like, sometimes somewhat narrowed, sometimes expanded posteriorly; the umbones are situated between the anterior \(1/3—1/5\) of the shell length, depending on the greater or lesser elongation of the shell,—moderately projecting above the hinge margin, convergent, weakly bent forward; the hinge margin either straight, then completely parallel to the lower margin, or slightly bent; the anterior margin shortened and rounded; the lower margin straight or weakly bent (convex, L. Kh.); the posterior margin rounded and more or less beveled; all angles rounded. Growth of the shell is uneven: during growth the shell elongates more at the posterior end than at the anterior; therefore at the posterior end the growth layers are coarse, uneven, and broad, while at the anterior they are crowded, thin, and more uniform; as a result of such uneven growth, the form of the shell becomes very distinctive, especially at the posterior end, where the uneven growth layers diverge in the form of ledges from the hinge margin backward and downward; the same stepped arrangement of the growth layers is also observed below the shell. The shell, in addition to coarse growth layers, is covered with very fine concentric striae” (see synonymy). In addition to this diagnosis, Amalitskii gives complete measurements of four specimens (see below, the table of metric ratios).

Fig. 20. Palaeanadonta cf. castor Eichw. Enlarged.

Description. In our collection there is one specimen, representing an impression of a left valve, very reminiscent of Eichwald’s species. The valve is developed in length, slightly expands posteriorly; the hinge margin is straight, constituting 0.78 of the length of the valve. The posterior margin is straight, but joins the hinge margin rather smoothly, forming an angle of \(120^\circ\). The ventral margin is weakly convex, without a sinus; it joins the posterior margin with a distinct break, owing to which the lower posterior angle is clearly expressed, measuring about \(80—90^\circ\). The ventral margin joins the anterior margin smoothly, but the anterior end—rather long—is narrowed, because the hinge margin in front of the umbo is considerably lowered. The greatest height is 0.47 of the length of the valve. The umbo is located at a distance of 0.22 of the length of the valve from the anterior end and, apparently, does not project above the hinge margin. The surface is covered with rather few coarse, and in the intervals between them—with dense fine concentric lines. The relief of the valve has not been preserved.

Metric ratios:

L	l	l′	H	h	α	\(l/L\)	\(l'/L\)	\(H/L\)	\(L/B\)	No. of specimen and locality
18	14	4	8,5	7,7	120°	0,78	0,22	0,47	0,91	\(\dfrac{\mathrm{XXI}}{3}\), r. Tom, 21
32	21	8	12	—	—	0,66	0,25	0,38	—	Palaeonodonta castor Eichw., Amalitskii, see syn., p. 120
29	19	7	10	—	—	0,65	0,24	0,35	—	Palaeonodonta castor Eichw., Amalitskii, see syn., p. 120
20	13	4,5	9	—	—	0,75	0,22	0,45	—	Palaeonodonta castor Eichw., Amalitskii, see syn., p. 120
18	13	4,5	8	—	—	0,72	0,25	0,44	—	Palaeonodonta castor Eichw., Amalitskii, see syn., p. 120

Similarities and differences. The specimen described differs from the Kolchugino species of the genus Anthracomya by its long anterior end, narrowing anteriorly because the hinge margin in front of the umbo descends noticeably downward while remaining straight. In this respect our specimen recalls some (atypical) representatives of the species Anthracomya williamsoni Brown (for example, those figured by Ruvost: 21, pl. VIII, fig. 15). The Kolchugino representatives of A. williamsoni (as determined by Yanishevsky—32, 1016), however, differ from our specimen in having a strongly developed sinus of the ventral margin.

Closest of all are certain specimens of Palaeanodonta castor Eichw., namely those that possess a shell widening posteriorly, weakly developed umbones, and a not very blunt posterior dorsal angle, as for example the specimens figured on pl. IX, figs. 4 and 5 by Nechaev (20). As the above table shows, the metric ratios of our specimen and of specimens of Palaeanodonta castor close to it in size coincide almost exactly. Only the insufficiency of the material compels me to refrain from a final identification of our specimen with Eichwald’s species.

Distribution. Our specimen comes from outcrop 21. This exposure is isolated (see the section on Table II) and is usually assigned to the Ilyinskaya subformation. Unfortunately, an extremely scanty fauna has been collected from this exposure, from which it has been possible to identify only the single specimen described above. Similar specimens have not been found in other exposures.

In the European part of the USSR Palaeanodonta castor is distributed in the Lower and Upper Permian.

Palaeomutela microdonta n. sp.

Table IV, figs. 2—7. Figs. 21, 22.

Comp. 1901. Posidonomya concinna: Jones. Geol. Magaz., dec. IV, vol. VIII, p. 345, pl. XVI, fig. 18.

Comp. 1937. Abiella subovata (pars): Fedotov. Lamellibranch mollusks etc., p. 47, pl. X, figs. 1—12.

Diagnosis. Shell of medium size, considerably convex, apparently equivalved, inequilateral, slightly elongated in length, of rounded-triangular outline. The maximum height is 0,7 of the length and passes through the umbo. The anterior margin is broad; posteriorly the shell narrows; both the anterior and posterior margins are rounded; the angle at the umbo is about 110°. The ventral margin is broadly and regularly rounded, on the whole considerably convex, without any signs of a sinus; it joins smoothly with the anterior and posterior margins.

The umbones are broad, blunt, strongly raised above the hinge margin, prosogyrate; they are situated at a distance of \(2/5\) of the shell length from the anterior margin. The valves are evenly convex; the keel is absent. The greatest convexity is below and slightly behind the umbo. From the most convex part the surface of the valve gradually descends toward the umbo, the anterior, ventral, and posterior margins, and drops more steeply toward the posterior half of the hinge margin.

The hinge is of the taxodont or pseudotaxodont type: on the narrow hinge plate there are numerous very small vertical denticles.

The surface of the valves is covered with numerous fine concentric lines, of which a few are more sharply

Fig. 21. Palaeomutela microdonta n. sp.

Fig. 22. Palaeomutela microdonta n. sp. Crushed shell. Enlarged.

expressed than the others. In addition, the superficial layer of the shell always reveals a very fine radial-rayed structure, which is probably secondary and creates the impression of radial striation.

Metric ratios:

L	l′	H	H/L	l/L	γ	Specimen no. and locality
17	6.5	12	0.71	0.38	110°	XXIIIB/17a, R. Tom, outcrop No. 23.
15.5	6.5	12	0.77	0.42	105°	XXIIIB/17б, ″ ″ ″
16	6.5	11	0.62	0.41	110	XXIIIB/17в, ″ ″ ″
10	4	7	0.70	0.40	—	XXIIIB/17a, ″ ″ ″

Remark. I observed the hinge in Palaeomutela microdonta on a number of internal molds obtained artificially. As far as I was able to familiarize myself with

this hinge exhibits variations: in some specimens it consists of irregular denticles and tubercles and is close to the hinges of species of the genus Palaeomutela from the Permian deposits of the USSR; in other specimens the denticles of the hinge are more numerous (on one specimen I counted more than 30 of them on the posterior branch of the hinge margin) and regular, approaching in character the hinge denticles of nuculids (incidentally, similar small and regular denticles occur in some palaeomutelas—see 20, pl. IX, fig. 31c).

Next it is necessary to dwell on the radial structure of the surface layer of the shell. It is expressed quite distinctly in all specimens of P. micradonta that have preserved the shell, and, conversely, I could not discern it on the shells of other forms (Anthr. supraphillipsii, Anthr. subparallela) occurring together with P. microdonta. Therefore, in the given horizon, on the basis of the presence of this structure, even fragments of the shell of our species can be determined. Thus, even if such a structure is secondary (12, 435), caused by recrystallization of the shell substance, it nevertheless (with the indicated restriction to the given horizon) may serve as a diagnostic character, since it indicates certain features in the structure of the outer shell layer of P. microdonta that conditioned a definite type of recrystallization not characteristic of the shells of other species encountered in this horizon. I cannot attach universal significance to this character for two reasons: first, if this structure is not primary, then on shells of P. microdonta from other horizons it may fail to appear, since there may have been different conditions accompanying recrystallization; and secondly, a similar structure has been observed by other authors on Kuznetsk specimens assigned to the genus Posidonomya (12, 435; 32, 1019), although, as will be seen from the further account, some of the specimens formerly assigned to the genus Posidonomya probably belong to Palaeomutela microdonta.

In our hand specimens P. microdonta occurs as closed shells, crushed and flattened (pl. IV, fig. 5), as isolated valves that have very rarely preserved relief, and, along with them, as fragments of shells. The shell is preserved fairly often, but usually it is cracked and easily flakes off, leaving internal molds and impressions.

Similarities and differences. In external appearance P. microdonta strongly recalls representatives of the genus Carbonicola, to which I would probably have assigned our specimens had I not had the possibility of exposing the hinge. A particularly significant resemblance is observed with some western European specimens of Carbonicola turgida Bronn (10, pl. VIII; 21, 194): the dimensions, outlines, relief of the valves, and sculpture (even “very fine radiating striae”—10, 67) bring P. microdonta and C. turgida so close together that I find it difficult to indicate any differences between them. In this example it is appropriate to emphasize how inaccurate determinations of the representatives of the group of fossils described in the present work can be if these determinations are based only on external characters.^1

Those Permian Palaeomutelae of the European part of the USSR that possess subtriangular shell outlines (20, pl. IX; 2, Taf. XX—XXI) differ in most cases in smaller size, the presence of a keel and of a depression in front of it, and a less rounded ventral margin. Even the closest of them can easily be distinguished from P. microdonta. Thus P. umbonata Fisch. (20, 265) differs in its lesser convexity, an umbo more displaced toward the anterior margin, and an obliquely truncated posterior margin; the specimen of this species figured by Eichwald (5, pl. XXXIX, fig. 21) has, in addition, a distinct keel. P. ovalis Amal. (2, 169) has more rounded shell outlines, umbones more displaced toward the anterior margin, a less rounded ventral margin, and less numerous and more irregular denticles of the hinge margin.

Among the fauna of the Kolchugino Series available to me there are no forms with which P. microdonta would have to be compared if the shell of the latter were not crushed. But in most cases the shells of P. microdonta, like the shells of other species, prove to be completely crushed, flattened—

^1 It is of interest, incidentally, that in the figure showing the hinge of C. turgida (10, pl. VIII, fig. 9), one can see at the anterior end of the hinge margin 5–6 small vertical denticles.

into a lobe, and in this form they lose the characteristic subtriangular outlines and become oval, and sometimes almost round (Pl. IV, figs. 5–6; fig. 22). Impressions of such crushed shells of P. microdonta acquire an extraordinary resemblance to those specimens of the Kuzbass fauna that are known in the literature under the names Posidonomya subovata Jones and Posidonomya concinna Jones. The shells of these species in the uncrushed state are easily distinguished from shells of Palaeomutela microdonta (see the description of P. subovata), but impressions of crushed shells cannot always be distinguished.

Probably, further study of the fossil fauna of Kuzbass will provide sufficiently precise criteria for distinguishing crushed impressions of shells of the forms indicated; at present I cannot indicate these criteria.

Among the numerous specimens referred by D. M. Fedotov to the species Abiella subovata, those predominate which show complete similarity to the specimens of Palaeomutela microdonta that were at my disposal. It is true that, since the structure of the hinge in the specimens in D. M. Fedotov’s collection has not yet been established, their identity with my species may raise doubts. But an examination of this collection (Museum of the Central Scientific-Research Geological-Prospecting Institute) compels me to pose this question, the solution of which, it seems to me, may be obtained quite simply: among the specimens there are some (for example, those shown in figs. 10 and 11, Pl. X; museum nos. 778 and 779) which, in their state of preservation, are entirely similar to the specimens in my collection that made it possible to expose the impression of the hinge by carefully dissolving the shell in acid.

Holotype — XXIIIB/17a; allotypes: XXIIIB/17b (shell form); XXIIIB/17v; XXIIIB/17g (hinge); XXIIIB/17d (hinge); XXIIIB/17e; XXIIIA/13a (hinge); XXIIIB/17zh (crushed shell).

Distribution. Palaeomutela microdonta is massively developed in the lower parts of the Yerunakovskaya subformation (bed H) and is fairly common in the upper parts of the Ilyinskaya (bed 11–10). This form has also been found in outcrop 1 near the village of Ilyinskoe.

Palaeomutela cf. concinna Jones.

(See pp. 36 and 83).

The species concinna still has no exact diagnosis, and it has not yet been established to which genus it should be assigned. Jones (12, 435) gives only the following brief explanation to the figure depicting a fragment of a shell of this species: “Part of a large Posidonomya with numerous clear, narrow concentric ribs and fine parallel lines between them. A more complete specimen of this rounded-oval form measures 18 mm in height and 20 mm in length.” M. E. Yanishevsky (32, 1019), without giving a description of this species, provides a good photograph of a specimen which, according to that author, is in no way different from Jones’s original. This photograph shows a shell with an oblique hinge margin, widening anteriorly and narrowing posteriorly. I refer to the species concinna specimens similar to the one figured by Yanishevsky. Such specimens occur in my material among the fauna of the Leninsky mine and are described below. From the Ilyinsky section of the Kolchugino suite I have at my disposal only more or less deformed specimens, which are very similar to the figure given by Yanishevsky. The dimensions of these specimens are as follows:

length	8.5	7	8.5	8
height	6.5	5.5	6	6.5

These specimens come from outcrops 1, 11, and 15.

Assignment of the species concinna to the genus Posidonomya is impossible, since they show no features characteristic of this genus. In the fauna of the Kolchugino suite the closest genus is Palaeomutela, to which I provisionally assign this species.

Palaeomutela (?) tomiensis Rag.

Table III, figs. 11, 12. Fig. 23.

1. Posidonomya tomiensis: Ragozin. Lamellibranchs from coal-bearing deposits of the southern part of the Kuzbass, p. 12, pl. VI, figs. 5, 7.

Diagnosis. “The shell possesses a perfectly symmetrical valve. It has the form of an ellipse. The upper side of the ellipse is cut off by a straight hinge margin, the length of which is somewhat less than the total length of the valve. The umbo is sharply marked and rises as a triangle in the middle part of the hinge line. The length varies from 4 to 11 mm and the height from 3 to 8 mm. The surface is covered with fine concentric lines” (22, 12).

Fig. 23. Palaeomutela (?) tomiensis Rag. Enlarged.

Remarks. I have quite a number of specimens which should be assigned to Ragozin’s species on the following grounds: the shell is almost equilateral, of elliptical outline; the umbones occupy a central position on the hinge line and are raised high above the latter. However, these specimens require the following refinements to be made to the diagnosis given above: first, the hinge margin is not entirely straight—from the umbo it descends more or less distinctly toward the anterior and posterior margins; second, on the surface of the shell there are, in addition to fine concentric lines, sharp and deep wrinkles dividing the surface of the shell into convex concentric bands, on which the fine lines noted in the diagnosis are situated.

Metric ratios:

L	l	l′	H	l/L	l′/L	H/L	Specimen no. and locality
11.5	8	5.5	7	0.69	0.48	0.61	I/15, Tom River, outcrop no. 1.
13	9	6	9	0.69	0.46	0.69	I/7, ” ” ”
7.2	4.5	3.5	4.5	0.62	0.49	0.62	XV/15, ” ” 15.
10	7.5	4.5	7.5	0.75	0.45	0.75	XV/19v, ” ” ”

Plesiotypes: XV/19b and XV/19v (“straight” hinge margin); XV/15 (sculpture), I/15 (curved hinge margin), I/7, XII/3a, I/5a, I/5b.

Distribution. Palaeomutela tomiensis is rather common in outcrops 1 and 15, and has also been found in outcrop 12.

Posidonomya subovata Jones.

Table IV, figs. 8—10. Figs. 24—25.

1. Posidonomya subovata: Jones. Geol. Mag., dec. IV, vol. VIII, p. 434, pl. XVI, figs. 8—15.
   ? 1901. Anthracomya laevis, var.: ibidem, p. 434, pl. XVI, fig. 5 (non figs. 6—7).
   ? 1901. Anthracomya valensiensis: ibidem, p. 434, pl. XVI, figs. 16—17.
2. Posidonomya subovata: Yanishevsky. Izv. Geol. Kom., vol. 46, No. 9, p. 1020.
   non 1937. Abiella subovata: Fedotov. Lamellibranch mollusks etc., p. 47.

Diagnosis. The shell is somewhat elongated lengthwise, of a rounded-oval, sometimes almost circular outline; the dimensions rarely reach 10 mm in length. The greatest height passes through the umbo and amounts to 0.7—0.9 of the length of the shell.

The hinge margin is straight only behind the umbo; in front of the latter it bends smoothly downward, imperceptibly passing into the anterior margin. At its junction with the posterior margin the hinge margin does not form a distinct angle. The length of the posterior straight part of the hinge margin is, on average, 2/5 of the length of the shell. The direction of the hinge margin in front of and behind the umbo is determined by the greater development of the posterior auricle in comparison with the small rounded anterior auricle.

Fig. 24. Posidonomya subovata Jones. Enlarged.

Fig. 25. Posidonomya subovata Jones. Enlarged.

The posterior part of the shell is broader than the anterior. The anterior, ventral, and posterior margins are outlined by a smooth curve, but the posterior margin is sometimes somewhat straightened in its middle part.

The umbones are small, sharp, slightly raised above the hinge margin and only slightly displaced from the middle of the dorsal margin; the distance between the anterior margin and the umbones amounts to 2/5 of the length of the shell. The convexity of the valves is slight, regular; the greatest convexity is situated below the umbo, from where the surface of the valve gradually and smoothly lowers toward the summit of the umbo and toward the anterior, ventral, and posterior margins, but in the direction toward the auricles the surface of the valve descends much more abruptly, giving steep slopes that meet at the summit (beak) of the umbo and form a straight umbonal angle. The surface of the auricles is flat.

The sculpture consists of a few sharp, regular concentric wrinkles and dense, very fine concentric lines between them.

Metric ratios

L	l′	l″	H	γ	l′/L	l″/L	H/L	Specimen no. and locality
10	4.6	4.4	8	90°	0.46	0.44	0.80	XVII/9в, Tom River, exposure no. 17.
11	3.5	4.8	8	—	0.32	0.44	0.73	XXIIIA/28а, „ „ 23.
5	1.8	2	4.4	90°	0.36	0.40	0.88	XVII/8а, „ „ 17.

Remarks. I have considered it necessary to give a new, as complete as possible, diagnosis of Jones’s species, because this author has only an extremely schematic characterization of P. subovata, perhaps because Jones apparently had at his disposal only crushed specimens. At the same time, this form is apparently rather widely distributed in the Kuzbass, and therefore refinement of its diagnosis cannot but be considered desirable. Jones noted the presence in his specimens of a radial-fibrous structure; this structure is absent in our specimens of P. subovata, although it is quite distinct in Palaeomutela microdonta, which occurs together with them.

Similarities and differences. Uncrushed specimens of P. subovata are easily distinguished by their outlines from all other pelecypods of the Kolchugino suite. The situation is much more complicated with crushed shells and valves of this species: in such a state the characteristic outlines of the shell ears are not preserved, the difference in the width of the anterior and posterior margins is smoothed out, and the relief is lost; usually the shell acquires a regular, uniformly oval outline, more rarely an obliquely oval one. Such crushed shells of P. subovata can by no means always be distinguished from crushed shells of Palaeomutela microdonta and can easily be confused with other forms as well. Only with crushed shells in mind can one speak of the similarity of P. subovata to Edmondia punctatella, as Jones (s. l.), Hind (11, 148), and Yanishevsky (32, 1020) do. Nor can one agree with Hind’s opinion on the necessity of removing P. subovata from the genus Posidonomya (s. l.); on the contrary, the uncrushed shells of this species possess outlines very typically expressed and characteristic of shells of Posidonomya.

In our collection there is a large number of crushed shells and valves in no way differing from Jones’s illustrations of P. subovata. Judging by their dimensions and sculpture, Jones’s specimens figured by him under the name Anthracomya laevis var. and Anthr. valensiensis (see synonymy) apparently belong to the same species: differences in the outlines of crushed specimens will obviously depend on the different orientation of the shells with respect to the direction of the crushing force. In our collection, along with predominantly regular-oval forms, there are also obliquely oval crushed shells which I do not consider it possible to separate from Posidonomya subovata.

[It has already been noted above that the form described by D. M. Fedotov under the name Abiella subovata, which this author identifies with Jones’s species—Posidonomya subovata, in my opinion belongs to the species Palaeomutela microdonta. In figs. 3 and 8 of plate IV are given the holotype of Palaeomutela microdonta mihi and the hypotype of Posidonomya subovata designated by me; both specimens are almost undeformed and give a clear idea of the form of the shell. The profound difference between these two species is quite obvious. But at the same

the table gives illustrations of crushed shells, which in this condition largely lose the characters proper to these forms. The specimens figured by Jones as representatives of the species Posidonomya subovata are strongly deformed, and it is not impossible that some of them belong to another species; this question cannot be resolved without a redetermination of Jones’s specimens. Therefore I assign the name subovata to that species which makes it possible to retain unchanged Jones’s generic determination, fully restoring the species Posidonomya subovata Jones and giving this species an expanded description.

Representatives of Posidonomya subovata in the Kolchugino suite are apparently much less widespread than representatives of Palaeomutela microdonta. Of the specimens of Abiella subovata figured by Fedotov, only one (Table X, fig. 6; museum number 77) possibly belongs to the species Posidonomya subovata; the affiliation with this species of the specimen numbered 776 is more probable¹.

Pleznogites: $\dfrac{\mathrm{XVII}}{9\mathrm{в}},\ \dfrac{\mathrm{XVII}}{8\mathrm{а}},\ \dfrac{\mathrm{XXIIIA}}{28\mathrm{а}}$.

Distribution. This species is most widely distributed in exposure 17 (bed A in the lower part of the Ilyinskaya subsuite), where its most typical representatives are encountered. In smaller numbers this species has been found in higher horizons of the Ilyinskaya subsuite, and it reappears in large numbers in the lower part of the Erunakovskaya subsuite (bed H), but here the shells of Posidonomya subovata are crushed and deformed and therefore are not always distinguishable from other forms.

Posidonomya linguloides n. sp.

See p. 81

Only one specimen belongs to this characteristic species, described in detail below, in the fauna from the Ilyinsko-Erunakovsky section $\left(\dfrac{\mathrm{XVII}}{6\mathrm{е}}\right)$ — a core of a right valve; the characteristic features—isometry (length = width = 6 mm), a straight posterior margin perpendicular to the hinge margin, a flatly rounded anterior margin, and the almost symmetrical character of the shell—leave no doubt as to the assignment of this specimen to the species P. linguloides. The anterior margin of the valve being characterized is more evenly convex than in the Leninsky specimens. The locally preserved concentric sculpture does not differ in any way from the sculpture of the Leninsky specimens.

The described valve was found in exposure 17.

Fauna of the Leninsky Mine.

Anthracomya fedotovi n. sp.

(See p. 62).

Table III, fig. 1.

In cores from the roof of the Kamyshinsky bed there are seven valves belonging to this species. The relief of these valves has not been preserved; in outline and sculpture they do not differ in any way from the Erunakovsky ones, but they are smaller: the largest specimen is 5.2 mm long, the smallest 2.3 mm. The insufficiency of the material does not make it possible to decide whether we are dealing here with a special dwarf modification, or whether only juvenile individuals have happened to be present in our collection. The specimen figured by Jones (12) in fig. 1, Table XVI, under the name Anthracomya minima Ludw., is extremely

similar to ours. Owing to the small size of the specimens, and in some cases also to their deformation, exact measurements of certain elements are impossible, while the others are very difficult and cannot be made with the desired accuracy.

Metric relations

L	l	l′	H	h	l/L	l′/L	H/L	h/H	Specimen No.
3	—	0.8	—	1.8	—	0.27	—	—	30 l / a
3	1.8	0.7	2	1.8	0.60	0.23	0.67	0.90	30 l / б
2.3	1.5	0.7	1.4	—	0.65	0.30	0.61	—	30 l / в
4.8	—	1.2	3.3	2.7	—	0.25	0.68	0.82	32 l
5.2	—	1.5	—	—	—	0.29	0.56	—	37 l / a

Anthracomya fedotovi n. var. lata.

Table 2, fig. 11. Fig. 26.

Diagnosis. Shell of oval outline. The hinge margin is straight, constituting half the length of the shell. Although the posterior margin is strongly convex and the upper posterior angle very obtuse, the point of junction of the hinge and posterior margins is quite clearly marked. The ventral margin is strongly convex; its lowest point lies approximately at half the length of the shell; with the anterior and posterior margins it joins quite smoothly. The anterior and posterior margins are broadly rounded, the anterior somewhat narrower than the posterior. The greatest width passes approximately through the middle of the shell length, somewhat closer to the posterior margin; it exceeds 3/4 of the shell length. The umbo does not rise above the hinge margin and is situated at a distance of 0.17 of the shell length from the anterior margin. The sculpture consists of the usual concentric wrinkles and fine lines.

Fig. 26. Anthracomya fedotovi V. Tschern., n. var. lata. Enlarged.

Remarks. This form is so close to Anthr. fedotovi typ. that separating it as a distinct species does not seem advisable; at the same time it differs from typical Antr. fedotovi in a number of features. With respect to the general outline of the shell, variety lata represents a deviation opposite to that observed in variety producta (see p. 54).

L	l	l′	H	h	α	\(\frac{l}{L}\)	\(\frac{l′}{L}\)	\(\frac{H}{L}\)	\(\frac{h}{H}\)	Specimen No.
10.3	5	1.8	8	5.5	120°	0.48	0.17	0.78	0.69	31 l

Similarities and differences. From the typical form, the variety lata differs in its greater development in height and in a shorter hinge margin. The latter character brings it closer to the variety producta, but the latter is still less developed in height than the typical form. From the typical form and the variety producta, the variety described differs in having the umbo more displaced toward the anterior margin. For convenience of comparison, the most important metric ratios of all three forms are brought together in the following table:

Name	\(\frac{l}{L}\)	\(\frac{H}{L}\)	\(\frac{l′}{L}\)
Anthracomya fedotovi typ.	0.60	0.60	0.25
Anthracomya fedotovi var. producta	0.65	0.50	0.22
Anthracomya fedotovi var. lata	0.50	0.78	0.17

From the typical representatives of Anthr. fedotovi encountered together with the variety lata, our variety differs in its larger dimensions.

Occurrence: the single specimen (holotype 31 l) is enclosed in the roof of the Kamyshin seam.

Anthracomya sp., cf. A. obliqua n. sp.

Two specimens from the roof of the Kamyshin seam show considerable similarity to Anthracomya obliqua, but because of their considerable deformation I am not certain of their identity. They are brought close to the indicated species by the general development of the shell along the diagonal, with rounded ventral and posterior margins. Exact measurements are impossible: the length of one specimen \(\left(\frac{37\,l}{г}\right)\) is 4.6 mm, that of the other \(\left(\frac{34\,l}{a}\right)\) is 6 mm.

Anthracomya sp.

One incomplete specimen (36 l) and one strongly deformed specimen \(\left(\frac{34\,l}{б}\right)\) do not permit specific determination, but apparently stand closest to Anthr. fedotovi. Both specimens come from the roof of the Kamyshin seam.

Posidonomya linguloides n. sp.

Plate IV, fig. 11.

Diagnosis. Shell isometric, almost equilateral; in outline approaching a square, one side of which (corresponding to the anterior margin) is convex.

The hinge margin behind the umbo is perfectly straight; this pos—

The posterior part of the hinge margin constitutes \(2/5\) of the length of the shell. The middle part of the hinge margin bends downward directly from the umbo, passing smoothly into the anterior margin. The anterior auricle is rather broad, rounded; the posterior one is more developed, rectangular. The posterior margin is straight, directed perpendicular to the hinge margin, but the angle of their junction is rounded. The ventral margin is weakly convex, straight or almost straight in the middle part, perpendicular to the posterior margin; the right angle of their junction is rounded. The anterior margin is broadly rounded, passing smoothly into the hinge and ventral margins. The greatest height passes through the umbo and is equal to or slightly less than the length.

The umbones occupy a subcentral position on the hinge line, standing away from the anterior margin at a distance of \(2/5\) of the shell length. The umbones are rather broad, raised above the hinge margin; the umbonal angle is less than a right angle.

The greatest convexity lies below the umbo, from where the surface of the valve gradually descends toward the sides and the ventral margin, and more steeply toward the auricles, especially the anterior one. The general convexity of the shell is insignificant.

The surface of the valves is divided by rather sharp concentric grooves into narrow concentric bands, on which fine and dense growth marks are situated. These concentric elements of sculpture are intersected by very fine (barely perceptible to the naked eye), short (interrupted), irregular radial riblets.

Metric ratios

L	\(l'\)	\(l''\)	H	\(\frac{l'}{L}\)	\(\frac{l''}{L}\)	\(\frac{H}{L}\)	Specimen No.
6	2.5	2.3	6	0.42	0.38	1.00	21л
8	3.3	3.5	7.5	0.41	0.44	0.94	20л
7.8	3.4	3.4	7.5	0.43	0.43	0.96	28л

Remarks. This very characteristic form is represented in our collection by three specimens: one well-preserved right valve (holotype—22л) and two impressions of left valves. The name of this species is explained by a certain external similarity to representatives of the genus Lingula.

Similarities and differences. The present species differs so sharply from the other pelecypods of the Kolchugino suite that comparisons become superfluous. Likewise, descriptions of closely related forms are absent from all the literature available to me. There is a certain, very remote, similarity to the species Posidonomya lamellosa (see II, 1901, 34), but the differences even in this comparison are numerous and obvious.

Occurrence. All three specimens come from the dumps of the Kapitalnaya 1 mine.

Posidonomya subovata Jones,

(see p. 77).

In the shale from the roof of the Kamyshinskii seam there is one specimen, representing a small flattened left valve belonging to the species

Posid. subovata. Outline almost rounded; the posterior margin is somewhat wider than the anterior; the hinge margin is straight.

The specimen does not differ in any way from similar specimens from the Ilyinsko-Erunakovsky section, described in detail above. Specimen number—33 l.

Posidonomya sp.

In the dumps of the Kapitalnaya 1 mine, together with Posidonomya linguloides, three poorly preserved specimens were found which, in some characters, approach this species, but do not admit of exact determination. The specimens are broad in width, with an almost central position of the umbones; the ventral margin is flatly rounded, the anterior and posterior margins convex; in the outline of the hinge margin a certain resemblance to that of Posidonomya linguloides can be discerned, for which reason these specimens are provisionally assigned to the genus Posidonomya. Apparently they are representatives of some new form, since they differ substantially from all the other pelecypods in our collection (the central position of their umbones somewhat brings them close to the species Palaeomutela (?) tomiensis, but that species differs in the character of the hinge margin and in outline).

Palaeomutela (?) concinna Jones.

Pl. III, fig. 10. Fig. 27.

1. Posidonomya concinna: Jones. Geol. Mag. dec. IV, vol. VIII, p. 435, pl. XVI, fig. 18.
2. Posidonomya (?) concinna: Yanishevsky. Izv. Geol. Kom., vol. 46, No. 9, p. 1019, pl. LI, fig. 10.
   non 1937. Abiella concinna: Fedotov. Plate-gilled mollusks, etc., p. 45.

Diagnosis. Shell of suboval outline, developed lengthwise, widening anteriorly and narrowing posteriorly. The hinge margin is almost straight—from the umbones it descends slightly toward the anterior and posterior margins. With the posterior margin it joins quite smoothly; with the anterior, however, the junction, though also rounded, is quite distinct. The length of the hinge margin is 0.6 of the length of the shell. The anterior end is broad, bounded by a margin which is straightened in its middle part. The posterior end is longer and narrower than the anterior, outlined by a convex curve. The lower margin is rounded, smoothly joining with the anterior and posterior margins. The greatest height passes through the umbo and amounts to 0.7–0.9 of the length of the shell.

Fig. 27. Palaeomutela (?) concinna Jones. Enlarged.

The umbones occupy a subcentral position, being removed from the anterior margin by 0.4 of the length of the shell. The umbones are slightly raised above the hinge line. The valves are regularly convex, with the greatest convexity below the umbones.

The sculpture consists of sharp concentric grooves, the convex intervals between which are occupied by fine lines.

Remarks. The diagnosis given above is not exhaustive, since I have at my disposal only two specimens of this species, and these are not in entirely perfect preservation. The generic affiliation of this species has been discussed above.

Metric relationships

L	l	l′	H	1/L	l′/L	H/L	Specimen No.
5	3	2	4.5	0.6	0.4	0.9	35л/б
2.3	—	—	2	—	—	—	35л/а
11	7	4.5	8.5	0.64	0.41	0.77	Posidonomya (?) concina, Yanishevsky, 32, pl. LI, fig. 10.

Similarities and differences. Our specimens are completely identical to the specimen figured by Yanishevsky, differing only in their smaller dimensions. In this same respect they differ from representatives of the present species from the Il’insko-Erunakovsky section. Palaeomutela microdonta differs in its subtriangular outline, narrower anterior end, higher umbones, and more pointed posterior end. Palaeomutela (?) tomiensis differs in the elliptical outlines of the shell, the equilateral character of the latter, and the more central position of the umbones. Posidonomya subovata Jones differs in generic characters, in particular in its shell expanded backward. Well-preserved specimens of Palaeom. (?) concina are easily distinguished from all the above-named species, but if the specimens are crushed and deformed, they can easily be confused with one of these species. The relationship between Palaeomutela concinna and Edmondia punctatella has been analyzed by Yanishevsky (32, 1019).

[As already noted above, the scope and content of the species “concina” in the works of D. M. Fedotov is different; moreover, the specimens referred by the author to this species, in my opinion, belong to the genus Posidonomya and differ substantially from the specimen Posidonomya (?) concina, which was figured by M. E. Yanishevsky and which I have accepted as the type of the species concina because of the absence of a satisfactory characterization and illustration of this species by its author.]

Pleziotypes: 35л/б and 35л/а.

Locality—both specimens are contained in the core from the roof of the Kamyshinsky bed.

Palaeomutela nanella n. sp.

Diagnosis. Shell of extremely small size, strongly inflated, elongated, inequilateral, of suboval outline. Hinge margin not straight, smoothly joining with the anterior and posterior margins. Anterior end broadly rounded; posterior end somewhat narrower than the anterior, also rounded. Ventral margin strongly and evenly convex, without a sinus; the curve describing the anterior, ventral, and posterior margins is completely smooth. Maximum height passes through the umbo and amounts to almost 3/4 of the length of the shell. Umbo broad and blunt, high; situated at a distance of 2/5 of the shell length from the anterior margin. Valves regularly and evenly convex; greatest convexity below and slightly behind the umbo, whence

the surface of the valve is fairly steep, but smoothly descends in all directions. The surface of the shell is almost smooth; very fine and very weak concentric lines are perceptible only under strong magnification and with a certain direction of the light.

Metric relations

L	l′	H	\( \dfrac{l′}{L} \)	\( \dfrac{H}{L} \)	Specimen No.
1	0.4	0.7	0.4	0.7	\( \dfrac{30\,л}{г} \), holotype. \( \dfrac{30\,л}{е} \)
1.1	—	0.8	—	0.7	\( \dfrac{30\,л}{г} \), holotype. \( \dfrac{30\,л}{е} \)

Remarks. The exceedingly small dimensions of the specimens that served for establishing this species may suggest that in the present case we are dealing with early stages in the development of some other species, for example Palaeomutela microdonta. The differences (apart from size) may be regarded as differences of age order. However, even the smallest specimens of other species exceed the specimens characterized here several times in size, and in my collection there are no specimens intermediate in size. Therefore I describe the latter under a separate specific name, although, obviously, this species is for the time being provisional.

Three specimens belong to this species: a well-preserved left valve that served as the holotype \(\left(\dfrac{30\,л}{г}\right)\); an impression of a somewhat deformed right valve \(\left(\dfrac{39\,л}{е}\right)\); and a good, but incomplete impression of the same right valve \(\left(\dfrac{30\,л}{д}\right)\). On the first two specimens it can be seen that the most inflated apical-umbonal part (prodissoconch?) is separated from the less convex marginal rim by a sharp furrow; on the third specimen this furrow is weakly expressed.

Similarities and differences. From all other pelecypods, Palaeomutela (?) nanella differs in its exceedingly small size. In outline it occupies an intermediate position between Palaeomutela microdonta and Palaeomutela (?) concina: in the former the outlines are more subtriangular, in the latter—more rounded. In addition, Palaeomutela (?) nanella possesses a different character of sculpture. The subtriangular outlines, imparted to the shell by the high umbo, distinguish the specimens of Palaeomutela microdonta from the species described here. Palaeomutela (?) concina is distinguished by a less curved hinge margin; the posterior end of the shell in Jones’s species is also broader.

Occurrence. All three specimens of Palaeomutela (?) nanella are enclosed in the core from the roof of the Kamyshinskii bed.

Palaeomutela (?) sp.

Three incomplete specimens from the dumps of mine A differ from all the others in the character of their sculpture: the latter consists of dense, sharp, fine, not entirely regular concentric wrinkles, covering the surface of the valves throughout. It is impossible to form a clear idea of the outlines of the shell from these specimens.

Summary

1. In the present work descriptions and an analysis are given of the fauna of lamellibranch mollusks from the Kolchugino Series of the Kuzbass.

The fauna comes mainly from the Ilyinsko-Erunakovo section of this series on the Tom River. Here the fauna was collected in 11 outcrops; of these, the most interesting are six outcrops from the continuous section of the Ilyinskaya Subseries below the mouth of the Uskat River and two outcrops from the lower part of the Erunakovskaya Subseries below the mouth of the Surnekovaya River (see the section in Table C). The beds corresponding to these outcrops are designated in Table A (p. 47) from bottom to top by the letters A, B, C, D, E, F, G, H. From these outcrops a fairly abundant fauna was collected; the fauna of the lower part of the Ilyinskaya and the lower part of the Erunakovskaya subseries is represented most fully.

In addition, a small collection of pelecypods was collected in the dumps of the shafts of the Lenin mine.

1. Among the pelecypods of the Kolchugino Series, representatives of the genus Anthracomya Salter predominate decisively (in the broad sense of this genus, with the inclusion in it of Anthraconauta Pruvost). Of interest is the discovery in the pelecypod fauna of the Kolchugino Series of forms with a taxodont (or pseudotaxodont) hinge, which the author has referred to the genus Palaeomutela Amal.¹ Well-preserved specimens have been found, allowing the author to assert that representatives of the genus Posidonomya Bronn are present among the Kolchugino pelecypods.

The list of forms established in the collection studied, consisting of 23 names, is given on p. 39.

For each form a detailed diagnosis is given, and comparisons with closely related species are presented. The overwhelming majority of the species proved to be new.

1. In Table A (p. 47) the vertical distribution of pelecypods in the Ilyinsko-Erunakovo section is presented. This table shows that the following can be characterized faunistically:

a) the lower half of the Ilyinskaya Subseries;
b) the upper half of the Ilyinskaya Subseries;
c) the lower part of the Erunakovskaya Subseries.

For the lower part of the Ilyinskaya Subseries the following association of species is characteristic: Anthracomya lata n. sp., Anthr. obliqua, A. simplex n. sp., Anthr. porrecta n. sp., Palaeomutela (?) tomiensis Rag. The upper half of the Ilyinskaya Subseries is characterized by a smaller number of forms, which must be attributed to the less extensive collections of fauna in this part of the section. Characteristic of this upper part of the Ilyinskaya Subseries are Anthracomya trigonalis n. sp., Anthrocomya cf. wrighti Dix et Truem., A. tomiensis n. sp. The lower part of the Erunakovskaya Subseries is characterized by the species: Anthracomya supraphillipsii n. sp., A. subparallela n. sp., which are represented here by an enormous number of specimens.

In the upper part of the Ilyinskaya Subseries and in the lower part of the Erunakovskaya, the species Palaeomutela microdonta n. sp. is widely distributed.

1. The above-indicated distribution of pelecypods in the Ilyinsko-Erunakovo section of the Kolchugino Series and the subdivision, on the basis of this fauna, of the Ilyinskaya Subseries cannot at present be extended to the Kolchugino Series of the Kuznetsk Basin as a whole, and these data must be checked in some other complete section of the Kolchugino Series; however, the results obtained show the possibility of a faunistic characterization of individual horizons of this series by pelecypods.

2. The rocks containing the pelecypod fauna reveal a complete similarity to analogous deposits of Europe, which received from B. I. Chernyshev the name of the Carbonicola facies. In general, these are fine-grained clayey and carbonaceous-clayey sediments, sometimes with an admixture of fine sandy material. The corresponding rocks (the Carbonicola facies) in Europe and the Donbass—

¹ In 1927 Yanishchevsky (32, 102) indicated that he had one internal mold with a taxodont hinge, referred by this author to the family Nuculidae.

have a Carboniferous age. It is natural that, with the complete facies identity of the deposits of the Kolchugino Formation with these Carboniferous rocks of Europe, a certain similarity is also observed in the fauna of pelecypods contained in these rocks. For some species this similarity is so considerable that, by a number of previous investigators of the pelecypod fauna of the coal-bearing deposits of Kuzbass, these Kolchugino species were identified with the corresponding western European ones, and consequently the age of the Kolchugino Formation was determined as Carboniferous.

1. However, alongside this similarity, which is manifested in the external characters of certain forms, there is also a substantial difference between the fauna of the Kolchugino Formation and the Carboniferous faunas of the Carbonicola facies. Thus, our fauna includes the genus Palaeomutela, widely distributed in the Permian deposits of Europe and Africa, but unknown in the Carboniferous deposits of the Carbonicola facies. The anthracomyas of the Kolchugino Formation as a whole also show notable features distinguishing them from the European fauna of anthracomyas: namely, in our fauna, with one exception, representatives of the genus Anthracomya possessing a sinus on the ventral margin are absent, whereas in the European fauna such forms are predominant. Also absent is the group, very widespread in Europe, of anthracomyas with a long anterior end that narrows forward and becomes pointed.

Representatives of the genus Posidonomya are very distinctive and have no close analogues in the European fauna.

In general, it may be said that the pelecypod fauna of the given formation, while showing, in certain of its representatives, considerable similarity to European forms, possesses more substantial and more numerous features of difference from the European fauna.

1. The above-mentioned similarity in the facies character of the deposits of the Kolchugino Formation to the European Carboniferous deposits, which predetermined a similarity also in the fauna of these deposits, was the cause both of the incorrect identification of a number of species among the Kolchugino pelecypods with European ones, and of the erroneous determination, following from this, of the age of this formation as Carboniferous.

2. The pelecypod fauna of the Kolchugino Formation, because of its endemic character, presents great difficulties for determining its age. Nevertheless, the collection studied and described in the present article shows that those elements of this fauna which can be compared with Carboniferous European forms occupy in this fauna an entirely subordinate position, and that their role was previously greatly exaggerated. Alongside them there are more significant indications of a younger age for these deposits, namely the genus Palaeomutela, characteristic of the Permian deposits of Europe and Africa, and also a form very close, if not identical, to the species Palaeanodonta castor Eichw.

3. However, comparison of the pelecypod fauna of the Kolchugino Formation with the fauna of the above-mentioned Permian deposits is made extremely difficult by the fact that the latter belong to another facies, associated with red-colored rocks. Naturally, under these conditions their fauna too will differ substantially from the fauna of the Kolchugino Formation, even if they are synchronous.

But all the greater significance and all the greater interest attach to those features of similarity which we can discover when comparing the fauna of such different facies.

1. Since the pelecypod fauna of the Kolchugino Formation does not give a direct answer to the question of its age, it is necessary to approach the solution of this question by considering the totality of all available direct and indirect indications. These data are as follows:

a) the presence in the fauna under consideration of certain elements of the fauna even of the heteropic Permian deposits of Europe;

b) the absence in it of Carboniferous species that had been indicated earlier and that, in fact, are new forms, i.e. the absence in it of species common even with the isotopic Carboniferous deposits of Europe;

c) the position of the Kolchugino Formation at the very top of the stratigraphic column of the Paleozoic productive series of Kuzbass, and the presence in the lower parts of this series

(Balakhonka Formation) marine fauna of Upper Carboniferous (or Lower Permian) age;

d) the unanimous opinion of paleobotanists concerning the Permian age of the flora of the Kolchugino Formation.

On the basis of all these data, the question posed above is resolved as follows: the fauna of the Kolchugino Formation represents an example of a fauna characterizing Permian deposits of the Carbonicola facies.

Since such a fauna has not yet been studied or described in any detail, it is natural that new forms predominate among the Kolchugino pelecypods.

1. The results obtained make it possible to state with confidence that the pelecypod fauna of the coal-bearing deposits of the Kuzbass, when studied in detail, can yield a significant number of guide forms that will make it possible to resolve questions of stratigraphic correlation of the corresponding deposits in different areas of the basin. To this end, special work must be undertaken on the systematic collection and detailed study and description of this fauna.

List of References

1. Amalitskii, V. P.—Communication on Russian Anthracosidae. Proceedings of the Warsaw Society of Naturalists, May 21, 1891.

2. Amalizky, W.—Über die Anthracosien der Permformation Russlands. Palaeontographica. Bd. XXXIX. 1892.

3. Amalitsky, W.—Comparison of the Permian freshwater Lamellibranchiata from Russia with those from the Karoo System of South Africa. Quarterly Journ. Geol. Soc., v. I. 1895.

4. Bolton.—On faunal Horisons in the Bristol Coalfields. Quarterly Journ. Pal. Soc., v. XXII, 1911.

5. Eichwald, E.—Lethaea Rossica, 1860.

6. Etheridge, R.—Further contributions to British Carboniferous. Geol. Mag., N. S., dec. II, vol. IX, 1877.

7. Fomichev, V. D.—On the stratigraphy of the Kuznetsk Basin. Transactions of the Main Geological-Prospecting Administration, issue 28, 1935.

8. Gibson, W.—Coal in Great Britain. 1927.

9. Grabau, A. W.—Stratigraphy of China, pl. 1. 1923–24.

10. Hind, W. A.—Monograph of Carbonicola, Anthrocomya, and Najadites. Palaeontogr. Soc. 1894–96.

11. Hind, W. A.—Monograph of the British Carboniferous Lamellibranchiata. Palaeontogr. Soc. 1896–1904.

12. Jones, T. R.—On some Carboniferous Schale from Siberia. Geologic. Magas., N. S., dec. IX, vol. XIII. 1901.

13. Krotov, P.—Geological investigations on the western slope of the Solikamsk and Cherdyn Urals. Transactions of the Geological Committee, vol. IV, 1888.

14. Likharev, B. K.—On the question of the age of the fauna from the base of the coal-bearing sequence of Kuzbass. Problems of Soviet Geology, vol. V, 1935.

15. Likharev, B.—The Permian System. On the question of its extent and stratigraphy. Problems of Soviet Geology, vol. I, No. 3, 1934.

16. Ludwig, R.—Die Najaden der Rheinisch-Westphalischen Steinkohlenfаrmation. Palaeontographica. Bd XII. 1859.

17. Ludwig, R.—Süsswasser-Bewohner aus der Westphalischen Steinkohlenformation. Palaeontographica. Bd. XIII, 1861.

18. Ludwig, R.—Zur Palaeontologie des Ural’s. Süsswasser Conchylien aus der Steinkohlen-Formation des Ural’s. Süsswasser Conchylien aus dem Kalkstein des Rothliegen von Kungur. Palaeontographica, Bd. X. 18, 1861.

19. Neiburg, M. F.—Investigations on the stratigraphy of the Carboniferous deposits of the Kuznetsk Basin, 1930–1931. Transactions of the All-Union Geological-Prospecting Association, issue 348, 1934.

20. Nechaev, A.—Fauna of the Permian deposits of the eastern belt of European Russia. Transactions of the Society of Naturalists at Kazan University, vol. XXVII, issue IV, 1894.

21. Pruvost, P.—Les niveaux à lamellibranches d’eau douce dans le terrain houiller du Nord de la France. Annales Soc. Géolog. du Nord. V. XIII, 1913.

22. Ragozin, L. A.—Lamellibranchs from the coal-bearing deposits of the southern part of the Kuznetsk Basin. Transactions of the Scientific-Research Coal Institute Vostugol, series I, issue 1, 1931.

23. Ragozin, L. A.—Lamellibranchs of the Prokopyevsk suite of Kuzbass. Collection on the Geology of Siberia, 1933.

24. Ragozin, L. A.—Pelecypods of the Balakhon suite of Kuzbass. Transactions of Tomsk State University, vol. 88, 1935.

25. Samylkin, D. G.—Geological-prospecting work in the area of the Yerunakovo deposit of the Kuznetsk Basin in 1930. Bulletin of the All-Union Geological-Prospecting Association, vol. L, issue 88, 1931.

1. Chernyshev, B. I.—On new anthracomyi from the coal-bearing series of the Minusinsk Basin. Izvestiya Glavnogo geol.-razv. upr., vol. XIX, no. 10, 1930.

2. Chernyshev, B. I. Carbonicola, Anthracomya and Najadites of the Donets Basin. Trudy Glavn. geol. razv. upr., issue 72, 1931.

3. Usov, M. A.—Conference on the stratigraphy of the Kuzbass. Vestnik Zap.-Sib. geol.-gidro-geod. tr., issue 3, 1934.

4. Verneuil.—Palaeontologie de la Russie, 1845.

5. Venyukov, P.—Geological investigations in the northern part of the Kuznetsk coal basin in the summer of 1894. Trudy geologich. chasti kabineta, vol. I, issue 2, 1896.

6. Yavorsky, V. I.—The left bank of the Tom River between the villages of Mitina and Erunakova in the Kuznetsk Basin. Izv. Vsesoyuzn. geol.-razv. ob’edineniya, vol. L, issue 66, 1931.

7. Yanishevsky, M. E.—On some Pelecypoda and Ostracoda from the coal-bearing series of the Kuznetsk Basin. Izvestiya Geol. kom., vol. XVI, no. 9, 1927.

8. Yanishevsky, M.—Description of the fauna from the base of the coal-bearing series of the Kuznetsk Basin. Uchenye zapiski Leningr. gosudarstvennogo universiteta, vol. I, issue 1, 1935.

9. Zalessky, M. D.—Materials for the geology of the Kuznetsk coal basin. Observations on the age of the coal-bearing series of the Kuznetsk Basin. Materialy po obshchei i prikladnoi geologii, issue 39, 1926.

*35. Clift, S. G. and A. E. Trueman.—The Sequence of Non-Marine Lamellibranches in the Coal Measures of Nottinghamshire and Derbyshire. Q. J. G. S. Lond., vol. 85, no. 337, 1929.

*36. Davies, I. H. and Trueman, A. E.—Revision of the Non-Marine Lamellibranches of the Coal Measures and a Discussion of their Zonae Sequence, Q. J. G. S. Lond., v. 83, 1927.

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Explanation of the Plates

Plate I.

Fig. 1. Anthracomya supraphillipsii n. sp. R. Tom, outcrop 23. Specimen $\dfrac{\mathrm{XXIIIA}}{11}$, holotype.

Fig. 2. Idem. R. Tom, outcrop 23. Specimen $\dfrac{\mathrm{XXIIIB}}{26}$.

Fig. 3. Idem. R. Tom, outcrop 23. Specimen $\dfrac{\mathrm{XXIIIA}}{2a}$.

Fig. 4. Anthracomya tscherryschewi n. sp. R. Tom, outcrop 16/17. Specimen $\dfrac{\mathrm{XVI}}{8}$, holotype.

Fig. 5. Idem. R. Tom, outcrop 15. Specimen $\dfrac{\mathrm{XV}}{3a}$.

Fig. 6. Idem. R. Tom, outcrop 16/17. Specimen $\dfrac{\mathrm{XVII}}{10v}$.

Fig. 7. Anthracomya n. sp., cf. A. wrighti Dix et Tr. R. Tom, outcrop 11. Specimen $\dfrac{\mathrm{XI}}{7}$.

Fig. 8. Anthracomya trigonalis n. sp. R. Tom, outcrop 10. Specimen $\dfrac{\mathrm{X}}{1a}$, holotype.

Plate II.

Fig. 1. Anthracomya porrecta n. sp. R. Tom, outcrop 16/17. Specimen $\dfrac{\mathrm{XVII}}{10d}$, holotype.

Fig. 2. Anthracomya subparallela n. sp. R. Tom, outcrop 23. Specimen $\dfrac{\mathrm{XXIIIA}}{23a}$, holotype.

Fig. 3. Idem. R. Tom, outcrop 23. Specimen $\dfrac{\mathrm{XXIIIA}}{8b}$.

Fig. 4. Idem. R. Tom, outcrop 23. Specimen $\dfrac{\mathrm{XXIIIA}}{22}$.

Fig. 5. Anthracomya obliqua n. sp. R. Tom, outcrop 15. Specimen $\dfrac{\mathrm{XV}}{17a}$, holotype.

Fig. 6. Idem. R. Tom, outcrop 15. Specimen $\dfrac{\mathrm{XV}}{7a}$.

Fig. 7. Idem. R. Tom, outcrop 15. Specimen $\dfrac{\mathrm{XV}}{20a}$.

Fig. 8. Anthracomya similis n. sp. R. Tom, outcrop 16/17. Specimen $\dfrac{\mathrm{XVII}}{10e}$, holotype.

Fig. 9. Anthracomya jedotowi n. sp. R. Tom, exposure 15. Specimen $\dfrac{XV}{13}$.

Fig. 10. Idem. R. Tom, exposure 16/17. Specimen $\dfrac{XVII}{1a}$.

Fig. 11. Anthracomya jedotowi var. lata. Lenin Mine, roof of the Kamyshinskii seam. Specimen 31 l, holotype.

Plate III.

Fig. 1. Anthracomya jedotowi n. sp. Lenin Mine, roof of the Kamyshinskii seam. Specimen $\dfrac{30l}{6}$.

Fig. 2. Anthracomya jedotowi var. producta. R. Tom, exposure 15. Specimen $\dfrac{XV}{5b}$, holotype.

Fig. 3. Anthracomya tomiensis n. sp. R. Tom, exposure 11. Specimen $\dfrac{XI}{4a}$, holotype.

Fig. 4. Anthracomya simplex n. sp. R. Tom, exposure 16/17. Specimen $\dfrac{XVII}{4a}$, holotype.

Fig. 5. Idem. R. Tom, exposure 16/17. Specimen $\dfrac{XVII}{2a}$.

Fig. 6. Anthracomya lata n. sp. R. Tom, exposure 15. Specimen $\dfrac{XV}{18}$, holotype.

Fig. 7. Idem. R. Tom, exposure 15. Specimens $\dfrac{XV}{7v}$ and $\dfrac{XV}{17g}$.

Fig. 8. Anthracomya n. sp., cf. A. curtata Brown. R. Tom, exposure 15. Specimen $\dfrac{XV}{3b}$.

Fig. 9. Palaeanodonta cf. castor Eichw. R. Tom, exposure 21. Specimen $\dfrac{XXI}{3}$.

Fig. 10. Palaeomutela (?) concinna Jones. Lenin Mine, roof of the Kamyshinskii seam. Specimen $\dfrac{35l}{6}$.

Fig. 11. Palaeomutela (?) tomiensis Rag. R. Tom, exposure 15. Specimen $\dfrac{XV}{12v}$.

Fig. 12. Idem. R. Tom, exposure 1. Specimen $\dfrac{I}{15}$.

Plate IV.

Fig. 1. Anthracomya n. sp. R. Tom, exposure 15. Specimen $\dfrac{XV}{5g}$.

Fig. 2. Palaeomutela microdonta n. sp. Undeformed left valve. R. Tom, exposure 23. Specimen $\dfrac{XXIIIB}{17b}$.

Fig. 3. Idem. R. Tom, exposure 23. Specimen $\dfrac{XXIIIB}{17a}$, holotype.

Fig. 4. Idem. Deformed shell from the side of the hinge margin. R. Tom’, outcrop 23. Specimen $\dfrac{\mathrm{XXIIIB}}{17\ \mathrm{г}}$.

Fig. 5. Idem. Crushed shell. R. Tom’, outcrop 23. Specimen $\dfrac{\mathrm{XXIIIB}}{17\ \mathrm{д}}$.

Fig. 6. Idem. Impression of a crushed shell with the hinge preserved. R. Tom’, outcrop 23. Specimen $\dfrac{\mathrm{XXIIIA}}{13}$.

Fig. 7. Idem. Impression of a deformed left valve. R. Tom’, outcrop 1. Specimen $\dfrac{1}{16}$.

Fig. 8. Posidonomya subovata Jones. Undeformed right valve. R. Tom’, outcrop 16/17. Specimen $\dfrac{\mathrm{XVII}}{9\ \mathrm{a}}$.

Fig. 9. Idem. Right valve from the inner side. R. Tom’, outcrop 23. Specimen $\dfrac{\mathrm{XXIIIB}}{30}$.

Fig. 10. Idem. Impression of the left valve. R. Tom’, outcrop 16/17. Specimen $\dfrac{\mathrm{XVII}}{3\ \mathrm{б}}$.

Fig. 11. Posidonomya linguloides n. sp. Right valve. Leninskii mine, Kapital’naya 1 shaft. Specimen 22 л, holotype.

Table 1

1

2

3

5

4

6

8

7

Table 2

1  2

5  6  3

7  8  4

9  10  11

Table 3

1

2

3

4

5

6

8

7

11

9

10

12

Table 4

1 2 3

4 6

5 7 11

8 9 10

1. On the label of this specimen it is stated that it is figured in the work of D. M. Fedotov (42) as fig. 9 in Table X; this is incorrect: fig. 9b depicts another specimen, apparently belonging to Palaeomutela microdonta. ↩↩↩↩↩↩↩↩↩↩↩

2. [In 1937, as already noted above, the presence of this genus among the pelecypods of the coal-bearing deposits of the Kuzbass was established by D. M. Fedotov]. ↩↩