Lower Devonian Spiriferidae of the Northern Altai

L. L. Khalfin

Introduction

The family of spiriferids, within the Devonian fauna of Siberia, plays a very important role and forms a number of groups that have guiding significance for stratigraphic conclusions. Such groups for the upper half of the Middle Devonian are the genus Indospirifer Gr., the group Hysterolites cheehiel Kon., the group Lamellispirifer mucronatus Conr., the group Spirifer martianoffi Stuck.; for the Upper Devonian—the genus Gürichella Paeck., the group Spirifer bouchardi Rig., the group Cyrtospirifer disjunctus Sow. Having a wide horizontal distribution in Siberia, these groups, for the most part sufficiently well studied, readily make it possible to decide the question of the age and correlation of the corresponding deposits of various districts of the Sayano-Altai region. Spiriferids could have no lesser significance for the stratigraphy of the Lower Devonian as well, but, unfortunately, the Lower Devonian fauna of Siberia in general, and the group that interests us at present in particular, have been studied extremely poorly; our information in this field is almost exclusively limited to data from the monograph of Petz (1901), which cites seven species of spirifers from the Lower Devonian deposits of the Kuzbass, predominantly of the Bohemian type. If to what has been said we add that, within the Lower Devonian fauna of Siberia, indigenous groups enjoy a very wide (if not predominant) development, which can be used for stratigraphic conclusions only after their detailed study, then the difficulties encountered in a number of cases by Siberian geology when it deals with deposits of the lower half of the Devonian will become clear. The practice of recent years in the work of geological institutions of Siberia shows that fauna collected in the process of geological surveying, usually in small quantity and more or less accidentally, does not provide any convincing age indications if it does not include representatives of cosmopolitan or already studied Siberian groups of fossils; naturally, this cannot but affect the quality of geological maps and reports. With the aim of at least partly filling the indicated gap with respect to the Lower Devonian, a description of the Lower Devonian spiriferids of the Northern Altai is given below.

In the Northern Altai, Lower Devonian deposits with a rich fauna were discovered not long ago at three localities:

1) near the village of Kuyagan on the Peschanaia River (Kondrat’evskaya hill);
2) near the village of Aleksandrovka in the basin of the Bol’shaya Tikhaya River (Medvedev ravine);
3) near the settlement of Kireevsky in the basin of the Anuy River (Ganin spring).

The geological conditions and the general characteristics of the fauna of these localities were published by me (1935) in a preliminary communication on the Devonian of the Altai; a more precise stratigraphic analysis of the deposits of Kondrat’evskaya Sopka and Medvedev Log was given by me (1938) in an article devoted to the pelecypod fauna from these localities.

Representatives of the family Spiriferidae are distributed in the deposits of all three localities, but this distribution is very uneven, which accords with the stratigraphic and facies differences of these deposits. Spiriferids are most numerous in the fauna of Medvedev Log, where they constitute one of the quantitatively predominant groups; the spirifers of Medvedev Log form an endemic association of forms and are represented exclusively by new species not encountered in the other two localities. In the deposits of Ganin Spring the spiriferids are monotonous (two species), but rather common and provide important indications for stratigraphic and geographic conclusions. Finally, in the fauna of Kondrat’evskaya Sopka this group of brachiopods occupies a completely subordinate position, being represented only by single specimens of five different species.

DESCRIPTION OF SPECIES

Spiriferidae of Ganin Spring

Genus Eospirifer Schuch.^1)

Within the genus Eospirifer Schuch. there is a well-defined group of forms very close to one another, possessing a nonplicate shell and, in the adult state, reaching very considerable dimensions. They are grouped around Spirifer togatus Barr., and some of them are regarded by certain authors as varieties, and sometimes also as synonyms, of this Bohemian species. The most important representatives of this group are Eospirifer togatus Barr., Eospirifer secans Barr., Eospirifer subsinuatus A. Roem., Eospirifer davousti Vern., Spirifer radiatus Sow. of American authors, Eospirifer turiensis T. Tschetgn., Eospirifer togatoides Paeck.

This group is developed in the Upper Silurian and Lower Devonian, chiefly in the lower part of the Eodevonian. I know of only one instance in which the presence of a representative of this group—namely Eospirifer davousti—has been indicated in the lower horizons of the Middle Devonian; I have in mind D. V. Nalivkin’s indication of the presence of this species in the lower horizons of the Middle Devonian of Fergana (1930, 111). I consider it necessary to dwell on this indication. D. V. Nalivkin includes Eospirifer davousti in the fauna of the Lyaglyan type (p. 1, 168), which is characterized by a mixture of Lower- and Middle Devonian forms (with the latter predominating) and to which, chiefly on the basis of such forms as Productella subaculeata Murch. var. mesodevonica Nal., Stringocephalus burtini Defr. var. orthocephala Nal. and Calceola sandalina Lam., D. V. Nalivkin assigns an Eifelian age. Turning to the lists of the Lyaglyan fauna by localities of its occurrence (pp. 1, 2, 5), we find that Stringocephalus burtini var. orthocephala is nowhere found together with Eospirifer davousti, although in various outcrops each of these forms was found in a large number of specimens. Calceola sandalina was found in a single specimen, the identification of which is accompanied by a question mark (p. 1, 1). If to this it is added that the indications concerning the collecting conditions of the Lyaglyan fauna are limited—

^1) Not having at my disposal some of the more recent literature on the classification of the spiriferids, I adhere to the classification proposed by Schuchert and Le Vene (1929), accepting the scope of the genera encountered in the Lower Devonian of the Altai in accordance with the proposals of these authors.

…are supported by the remark concerning the fauna of localities 333 and 999: “both collections were made in one and the same suite and in identical limestones,” from which it may be concluded that the collections were not bed-by-bed; thus, naturally, the question arises of the possible origin of the Lower and Middle Devonian forms of the Lyaglyan fauna from different horizons of the Lower and Middle Devonian. Thus, the indication noted above of the presence of Eospirifer darousti (together with a number of other Lower Devonian forms) in the Eifelian deposits of Central Asia requires additional confirmation.

In Siberia, representatives of the cosmopolitan group of eospirifers under consideration were, until recently, unknown. In my preliminary communication on the Devonian fauna of the Altai I noted (1935, 30) the presence, in the Lower Devonian deposits of Ganin Spring, of a form which I identified with Eospirifer subsinuatus A. Roem.; on the basis of a detailed study of more extensive material I have come to the conviction that this identification is incorrect: in the deposits of Ganin Spring a form is very widespread which is very close to Eospirifer subsinuatus and Eospirifer togatus, but not identical with these species, and which I distinguish as a new species—Eospirifer pseudotogatus.

Eospirifer pseudotogatus n. sp.

Plate I, figs. 1–8. Fig. 1–3.

1. Spirifer subsinuatus: Khalfin. Materials on the stratigraphy of the Devonian deposits of the Altai, p. 30, pl. VIII, fig. 4.

Specific characters. A large shell of transversely elliptical outline, with valves slightly and equally convex. The hinge margin is short, comprising approximately \(3/5\) of the greatest width of the shell, and at the ends, with a smooth bend cutting off the cardinal angles, passes into broadly rounded lateral margins. The anterior margin as a whole is rounded, with its middle part somewhat projecting, owing to the strong development of the fold and sinus, corresponding to the arcuate, dorsally directed bend of the anterior commissure. The line of greatest width passes through the middle between the hinge and anterior margins.

The ventral valve is moderately convex, with a sharp, incurved beak. The area is moderately developed, triangular, concave, and not sharply delimited. The delthyrium is triangular, completely open. The sinus begins at the very beak; at first it is narrow and rather deep, toward the anterior margin it widens greatly, and near the anterior margin its width reaches \(1/2\) the width of the shell; the depth of the sinus toward the anterior margin increases much less than its width, as a result of which the sinus on the anterior part of the shell has the character of a broad and flat depression. The sides of the sinus, rather steep in the posterior part, become very gently sloping and rounded on the anterior half; because of this the sinus in its posterior part is clearly delimited from the lateral parts of the valve, while anteriorly the boundary between it and the lateral parts becomes effaced. The bottom of the sinus is rounded; the tongue is broad, arcuate.

In the ventral valve there are very small teeth and strongly developed, thick, divergent dental plates. With growth of the shell there occurs an intensified deposition of calcareous material on the inner side of each plate, and this process involves only the posterior half of the plates, within the area and somewhat below the latter; as a result, the delthyrial cavity in its apical part is transformed into a narrow slit (fig. 1), and on the internal molds of old shells the muscle field in its posterior part assumes the character of a narrow ridge, widening dors—

…sally (Pl. I, figs. 5–6). But even in the oldest individuals this process never leads to contact between the dental plates, and the latter remain separated by a narrow slit which nevertheless reaches the bottom of the valve. At the same time there is abundant deposition of skeletal substance within the umbonal cavities, filling the apical parts of the latter. Therefore, whereas in younger individuals (Pl. I, fig. 3), on internal moulds of the ventral valves the umbonal cavities are expressed as sharply conical casts, the apices of which come close to the beak of the valve, in older specimens the apices of these conical casts prove to be truncated (Pl. I, fig. 6). Septa and a delthyrial plate are absent.

The ventral muscle field has a subcordate form owing to the bilobate character of its anterior margin, but its outlines are very weakly expressed and at times indistinguishable. The muscle impressions are shallow and on the moulds do not form a strongly projecting boss. When preservation is good, four portions can be distinguished on the muscle field (Fig. 2): the posterior triangular part of the field, confined to the part of the delthyrial cavity narrowed (owing to additional deposition of skeletal material on the dental plates), represents a smooth impression of the adjustor muscles; the anterior part is occupied by two broad diductor impressions of subelliptical outline, between which lies a narrow impression of the adductor muscles; the impressions of the diductors and adductors are covered by fine, faintly visible fan-shaped striation. All these parts of the muscle field are weakly delimited, but when preservation is good they are quite distinguishable. Within the umbonal cavities, on the inner surface of the valve, punctate ovarian impressions are visible.

Fig. 1.*)

The dorsal valve is moderately convex, with a beak slightly raised above the hinge line; beneath the beak there is a triangular open notothyrium, formed by “straight walls”—socket walls sensu Hall. The saddle, beginning at the very beak, is clearly expressed along its entire length and at the anterior margin constitutes \(^{2}/_{5}\) of the width of the shell; it is flatly rounded in character, low, with steep sides sharply separating it from the rest of the valve surface. The cardinal process is completely resorbed. The muscle field is not expressed.

Fig. 2.

The outer surface of the valves is covered with fine, threadlike radial costellae, increasing in number by dichotomy. On internal moulds of the valves this fine sculpture is usually noticeable only on the anterior half and near the lateral margins.

Growth marks are sharp, few in number.

Dimensions:

*) Explanation of the figures in the text—see p. 199.

Remarks. Because of the nature of preservation of the material available to me (cores and impressions of almost exclusively isolated valves), I cannot give a characterization of the structure of the brachidium in Eospirifer pseudotogatus.

Special remarks must be made concerning the area of the dorsal valve (Fig. 3). On one of the specimens (allotype \(\frac{\mathrm{KT}-9_5}{14}\)) its impression has been preserved; the latter makes it possible to establish the presence of an open notothyrium, the walls of which are “straight walls” in Hall’s terminology. Along the sides of these “straight walls,” on the area, there are long and narrow depressions, beginning almost at the beak and occupying the greater part of the area on both sides of the notothyrium. Similar structures are figured in the monograph of Hall and Clarke in Eospirifer radiatus Sow. (1894, pl. XXI, fig. 13), in Spirifer oweni Hall (ib., pl. XXII, fig. 3), in Spirifer granulosus Conr. (ib., pl. XXIII, fig. 3), and in several other forms. Hall and Clarke call these depressions dental sockets. However, the form and position of these depressions do not correspond to the form and position of the teeth of the ventral valve; only the lower expanded parts of these depressions, clearly visible in the above-cited figures in Spirifer granulosus and Eospirifer radiatus, can be regarded as the actual dental sockets. The remaining narrow part of these depressions, lying on the area along the sides of the notothyrium above the dental sockets, is apparently formed in the process of displacement of the latter with the growth of the shell. I call this element the trace of the dental sockets.

Fig. 3.

In Eospirifer pseudotogatus the actual dental sockets are not expressed, but the trace of the dental sockets is quite distinct. This corresponds to the extremely weak development of the teeth in adult individuals of this species, and from this we are entitled to conclude that in the course of growth the teeth in Eospirifer pseudotogatus are very strongly reduced.

This reduction of the teeth stands in sharp contradiction to the strong development and thickening of the dental plates in adult individuals of Eospirifer pseudotogatus. The latter compels me to adhere to the opinion of Thomas and other authors (Miloradovich, 1937, 504), who deny a genetic dependence between the teeth and the dental plates and regard the latter as an apparatus strengthening the areal part of the ventral valve.

Similarities and differences. Very close forms are the Bohemian Eospirifer togatus Barr. and Eospirifer secans Barr.; both these species differ in more convex valves, a longer hinge margin, and a more developed and sharply bounded ventral area; moreover, in these Bohemian forms the line of greatest width lies close to the hinge margin. Eospirifer togatus is further distinguished by a sharply bounded, flat-bottomed sinus; in the character of the saddle and sinus the Altaian form stands closer to Eospirifer secans. Also very close is Eospirifer subsinuatus A. Roem. (Kayser, 1878, 162), distinguished chiefly by weakly rounded, clearly expressed cardinal angles and, judging from the figure given by Kayser (l. c., Taf. XXI, Fig. 7), by a sinus beginning only at some distance from the beak. The latter, as indicated by Paeckelmann, distinguishes A. Roemer’s species also from Eospirifer togatoides Paeckelmann (1925, 128)—a form in all respects extremely close to Eospirifer pseudotogatus, but distinguished by a very long hinge margin and, correspondingly, a long ventral area. Eospirifer davousti Vern., identical in the opinion of Barrois (1889, 141) and Scupin (1900, 215) with Eospirifer subsinuatus Roem., is distinguished by a long hinge ...

margin, a distinctly delimited area, less rounded cardinal angles, and a less flat-topped sinus (Nalivkin, 1930, 110). Eospirifer turiensis Tschern. (Chernyshev, 1894, 56) is distinguished by a much more strongly inflated shell, a deep sinus, and a high saddle.

Distribution. Eospirifer pseudotogatus was found in a quantity of 16 specimens in one outcrop; at other points of the section along the Ganin key it was not encountered. Representatives of the genus Eospirifer are also absent from other localities of the Lower Devonian fauna of Altai.

The closest forms are developed chiefly in the Lower Devonian of Western Europe and, to a lesser degree, in the Upper Silurian.

Holotype:
$\dfrac{\mathrm{KG}-9}{14}$; allotypes: $\dfrac{\mathrm{KG}-9}{14}$ (area and teeth of the ventral valve, sculpture)

$\dfrac{\mathrm{KG}-9_{3}}{14}$ (dental plates, ventral muscular field), $\dfrac{\mathrm{KG}-9}{14}$ (dental plates and the delthyrial cavity of an old individual, ventral area), $\dfrac{\mathrm{KG}-9}{14}$ (structure of the dorsal area).

Genus Delthyris Dalman—Schuchert

I take the scope of this genus in accordance with Schuchert’s proposal, i.e., I consider the presence of a ventral septum an obligatory diagnostic character, the genotype of the genus—Delthyris elevata Dalm.—and the scope of the genus as corresponding to the lamellosi-septati group according to the classification of Hall and Clarke. As for the externally similar but ventral-septum-less group fimbriati-unispinei, in which these authors were inclined to see an analogue of the genus Delthyris Dalman (1894, 19), for this group the name Crispella Kozlowski (1929, 30), with the genotype—Spirifer crispus His., should be adopted.

In the deposits of the Ganin key this genus is represented by the species Delthyris perlamellosa Hall, quite identical with American specimens of this form and very close to Delthyris perlamellosa var. altaica Khalf., found in the deposits of Kondrat’evskaya hill.

Delthyris perlamellosa Hall

Table I, figs. 9—11; Table II, figs. 1—2. Fig. 4—6.

1. Spirifer perlamellosus: Hall. Pal. N. Y., vol. III, p. 201, pl. XXVI, figs. 1, 2.
2. Spirifer perlamellosus: Billings. Geol. Canada, p. 957, fig. 455.
3. Spirifer perlamellosus: Meek and Worthen. Geol. Surv. Illinois, vol. III, p. 384, pl. VII, fig. 9.
4. Spirifer perlamellosus: Hall and Clarke, Pal. N. Y., v. VIII, pt. II, pl. 35, figs. 7—13.
5. Delthyris perlamellosa: Schuchert. Bull. U. S. G. S., № 87, p. 207.
6. Spirifer perlamellosus: Schuchert and Maynard. Maryl. Geol. Surv., Low. Dev., p. 397, pl. LXIX, figs. 4—6.
7. Delthyris perlamellosus: Tansey. Fauna Bailey Is., p. 199, pl. L, figs. 41—49.

Description of specimens. Four ventral valves and four dorsal valves in the form of internal molds, partly incomplete and deformed; for one ventral and one dorsal valve there are also impressions of the external surface.

The shell is strongly developed in width, with cardinal angles drawn out into sharp points. The ventral area is moderately high, concave, sharply delimited; the delthyrium is completely open. The sinus begins at the beak, is deep, bounded by high folds, with a rounded bottom. The septum is thin and long—more than half the length of the shell; dent-

... plates are thin; in the apical part the septum projects slightly between them, without forming a spondylium (Fig. 4).

The dorsal area is very low, straight; the cardinal process is reduced (see below, “Remarks”); on the sides of the notothyrium there are deep, narrow, strongly diverging traces of dental sockets—their expansions in the lower part form the dental sockets. The traces of the dental sockets are separated from the notothyrium by thin and weak socket plates, on the inner sides of which are thickened traces of the attachment of the diductors. The surface of the latter is covered with longitudinal furrows. The bases of the crura are low, horizontally oriented, arcuately curved plates, with their convexity directed upward (see Fig. 6).

Fig. 4.

The outer surface of the valves is covered with dense, lamellar growth marks; on the plates there are thin radial striae that do not form needles. Radial folds are present in numbers of 4, more rarely 5, on each side of the saddle and sinus; sometimes a sixth fold is faintly indicated. The folds are high, with a somewhat rounded crest, separated by similar interspaces; the folds bounding the sinus are considerably larger than the remaining ones.

Dimensions:

Remarks. In the description given above, the saddle of our representatives of Delthyris perlamellosa has not been characterized, since in all specimens it is damaged and appears perfectly flat-topped; if this feature were really characteristic of the Altaian representatives of the described species, it would constitute some distinction from the American specimens, but it is more probable that in the present case we are dealing with the result of mechanical deformation of the saddle.

The species Delthyris perlamellosa shows considerable individual variability in a number of characters, in particular in the structure of the delthyrium. In Hall’s monograph (1859, pl. XXVI) a series of illustrations is given showing a completely open delthyrium in representatives of this species; in the later monograph of Hall and Clarke (1894, pt. II, pl. XXXV) American specimens of this species are figured, showing different stages and different forms of covering of the delthyrium: fig. 12 shows a convex plate closing the delthyrium from the sides and above; in fig. 10 the delthyrium is completely closed, and on the convex plate there is a round foramen; in fig. 11 the delthyrium is almost completely closed and also has a foramen. The plate closing the delthyrium is convex and bears no signs of a longitudinal suture, i.e., according to the terminology accepted by us, it should be called a pseudodeltidium, or a symphytium in Bückmann’s terminology. The specimens from the fauna of the Ganin Key have a completely open delthyrium. But the very close variety altaica of the species Delthyris perlamellosa found in the deposits of Kondrat’evskaya Sopka (see p. 196) shows in the structure...

the delthyrium is an interesting new detail (Table IV, fig. 12): the delthyrium is found to be closed in the upper part, without the formation of a foramen (as in the above-cited fig. 12 in Hall’s and Clarke’s monograph), but the plate closing it is flat, consisting of two parts separated by a distinct longitudinal suture, i.e., it has the character of a true deltidium or deltharium amplectens, but without a round foramen and with an opening in the lower part of the delthyrium. Thus, within the limits of a single species there are observed:

a) an open delthyrium;
b) a symphythium without a round foramen and with a deep notch below, entirely similar to the pseudodeltidium of Protremata (see Miloradovich, 1937, 515);
c) a symphythium with a round foramen above and a notch below;
d) a symphythium with a round foramen, completely closing the delthyrium;
e) a deltidium amplectens, but without a foramen and leaving the lower part of the delthyrium open.

Also deserving special note is the mode of attachment of the diductor muscles in the dorsal valve of Delthyris perlamellosa. In Figs. 5 and 6 are given copies of the illustration from the monograph of Hall and Clarke (1894, pl. XXV, fig. 13) and an illustration of the structure of the notothyrium in a specimen \( \frac{\mathrm{KG}-\mathrm{N}_3}{14} \) from the fauna of the Ganin key. The American specimen shows the attachment of the diductors to the inner sides of the dental plates; the corresponding areas of the latter have longitudinal grooving and are called

Fig. 5.                Fig. 6.

by Hall and Clarke the cardinal process, with which one can hardly agree. On our specimen (Fig. 6) the same details are present, but, in addition, between them there is a trace of a reduced cardinal process. Thus, it may be stated that in Delthyris perlamellosa a complete reduction of the cardinal process is observed; this is accompanied by a shift of the place of attachment of the diductors to the inner sides of the dental plates, where certain thickenings with longitudinal grooving arise (in the cited fig. 13 in the monograph of Hall and Clarke they are designated by the letter j). For these traces of the diductor muscles it is evidently impossible to retain the name “cardinal process,” and they may be called notothyrial impressions of the diductors.

Similarities and differences. Delthyris parlamellosa possesses strong variability not only with respect to the structure of the delthyrium, but also with respect to the height of the ventral area, the outlines of the shell, and the number of radial folds, as may readily be seen by examining the numerous illustrations of American representatives of this species (see the synonymy). The specimens described above are in every respect identical with those American specimens that are developed in width and provided with cardinal mucronations, a representative of which is figured by Hall (1859) in fig. 1, pl. 26. Perhaps such forms should be separated from the more isometric and rounded ones as a special variety (mucronata).

Delthyris perlamellosa var. altaica from the deposits of Kondrat’evskaya Sopka differs in having a larger number of folds (up to 9 on each side of the saddle and sinus) and a higher ventral area.

Distribution. In North America Delthyris perlamellosa is very widely developed in Lower Helderbergian deposits (Bailey limestone of southeastern Missouri, the New Scotland horizon of Maryland, etc.).

In the deposits of the Ganin Brook, 7 specimens of this species were found together with Eospirifer pseudotogatus.

Plesiotypes: \(\dfrac{\mathrm{KG}-\mathrm{N}_1}{14}\) (ventral valve—area, delthyrium, sculpture); \(\dfrac{\mathrm{KG}-\mathrm{N}_2}{14}\) (internal mold of ventral valve—tooth plates; septum); holotype—\(\dfrac{\mathrm{KG}-\mathrm{N}_3}{14}\) (internal mold and impression of dorsal valve—structure of the area, sculpture).

Spiriferidae of Medvedev Log

Spirifer Sow. s. l.

Our spirifers exhibit great diversity in the dimensions and outlines of the shell, as well as in certain other external details. On the basis of these differences I have distinguished nine forms of spirifers in the fauna of Medvedev Log, which, however, also possess a number of common characters. This applies above all to the sculpture: all our spirifers are characterized by large and flat, rather few radial folds, which are situated only on the sides of the saddle and sinus, so that the latter, as well as the parts of the valves adjoining the cardinal angles, remain smooth. At the same time, our spirifers are characterized by a more sharply expressed sculpture on the dorsal valve than on the ventral valve, on which the folds sometimes disappear completely: most internal molds of ventral valves appear entirely smooth, whereas the molds of dorsal valves are distinctly folded; this difference is also clearly expressed on impressions of the external surface of the valves. In a number of cases, on internal molds near the anterior and lateral margins, fine radial elements of the sculpture are visible; on the basis of these, however, it is not possible to determine precisely the nature of this fine sculpture of the external surface of the valves. This prevents assigning our spirifers to one or another genus or subgenus of the family. The genus Hysterolites is the closest in general character, but since the nature of the fine sculpture in our forms has remained undetermined, I prefer to leave them simply within the genus Spirifer sensu lato.

The type of coarse folding of the valves characterized above is inherent in all nine forms established among the spirifers of Medvedev Log. There is one more conspicuous feature uniting all our spirifers (with the exception of three specimens, mentioned below): this is the character of the saddle; about a hundred specimens of dorsal valves in my collection show one and the same character of the saddle, namely, the saddle begins at the very beak, is very sharply delimited from the lateral parts, is very broad on the anterior half of the valve, high, roof-shaped, with a sharp or slightly blunted ridge. Of the nine forms described below:

only the last two have a different character of the saddle; moreover, Spirifer cf. mischkei is represented in our collection by two specimens, and Spirifer cf. iberingi—by only one. With the exception of these three specimens, the remaining spirifers of Medvedev Log form a natural group of closely related forms, although in some external characters they also show considerable differences. As will be seen from the subsequent species descriptions, this group is an indigenous association of forms. And, taking into account this indigenous character of the entire group of spirifers of Medvedev Log, it may be supposed that the last three forms in the list given above will also prove, in the future, to be new species.

Apparently, common to all our spirifers is the presence of a thin, low, and short median riblet in the dorsal valve: on all internal molds of dorsal valves, when preservation is sufficiently good, a trace of this riblet is observed in the form of a thin and short groove situated on the crest of the saddle in the beakward part of the latter (see pl. III, fig. 3; pl. IV, fig. 6).

I do not find it possible, as I have already indicated above, to assign this group of Altai spirifers to any one of the known subgenera or narrowly understood genera of the family. Formally, guided by the outlines and coarse plication of the shells, one might find among our spirifers analogues of some Rhenish groups of spiriferids classified by Wedekind (1925, 198). Thus, Spirifer paucicostus and Spirifer pseudofallax could be assigned to the genus Acrospirifer Wdk., and Spirifer korovini and Spirifer rarus—to the genus Euryspirifer Wdk. However, this would be an artificial and essentially incorrect solution of the question for the following reasons: in the Rhenish Devonian the genera Acrospirifer and Euryspirifer are groups that do not coincide in time, whereas in the Altai Devonian isometric and winged species exist simultaneously and are linked by an intermediate form—Spirifer semicirculatus. This is a single group, genetically and stratigraphically, representing a local association and probably deserving separation into an independent taxonomic unit, all the more so because morphologically (small number of plications, their uneven development on the ventral and dorsal valves, character of the saddle) our spirifers possess a number of specific features.

Despite the fact that the spirifers of Medvedev Log constitute an indigenous group, they provide certain indications of the age of the corresponding deposits, and these indications do not diverge from what we have for other groups of the Medvedev Log fauna: the general character of our spirifers and the species-specific features of individual forms in a certain way bring our spiriferids closer to Lower Devonian representatives of this family, among which we also find the closest analogues of some of our forms.

Spirifer paucicostus Khalf

Pl. III, fig. 8; pl. IV, fig. 2

1. Spirifer paucicostus (partim): Khalfina, Materials on the stratigraphy of the Devonian deposits of Altai, p. 18.

Species diagnosis. The shell is isometric. The outline of the dorsal valve is semielliptical, with the hinge margin corresponding to the minor axis of the ellipse; in the ventral valve, above the hinge margin, a fairly high curved beak rises, beneath which a triangular concave area is situated. The greatest width of the shell passes near the hinge margin, but does not coincide with it, since the cardinal angles are distinctly rounded.

The ventral valve is strongly convex; the greatest convexity lies below the hinge margin and above the center of the valve. From the very beak begin—

…a narrow and deep sinus begins, possessing steep sides and a rounded bottom. On the internal molds, traces are visible of short, almost parallel dental plates, bounding in the posterior part a narrow and long muscular scar.

The dorsal valve is considerably convex, but less so than the ventral valve. The fold begins at the beak, is strongly developed, and is sharply delimited from the lateral parts of the valve; in form the fold is roof-shaped, but with a rounded crest; near the anterior margin the fold is considerably wider than the sinus.

The sculpture consists of broad, flat radial plications separated by narrower interspaces; on the ventral valve these plications are extremely weakly expressed and on the molds are usually not noticeable, whereas on the dorsal valve they are quite distinct also on internal molds. Number of plications: on the ventral valve, not counting the plications delimiting the sinus, three on each side of the sinus; on the dorsal valve, likewise on each side of the fold, three plications are clearly visible, sometimes a fourth is faintly indicated; thus, at least on the molds, on each side of the fold only approximately half of the lateral part of the valve adjacent to the fold is occupied by plications, while the other half, adjoining the hinge margin, is devoid of sculpture. Near the anterior margin the width of the fold is equal to the width of three, rarely four, adjacent plications. On the molds, a few sharp growth marks are noticeable.

Dimensions:

Similarities and differences. The closest form is Spirifer frequens Bubl., described by N. L. Bublichenko from the Devonian deposits of southwestern Altai, to which this author assigns an Eifelian age (1927, 1204); N. L. Bublichenko’s species is close in the outlines of the shell, has the same type of radial plication and the same character of the fold. The differences of our species are: a considerably more weakly expressed plication of the ventral valve, a smaller number of radial plications (3–4 in our species and 5–6 in Sp. frequens on each side of the fold), a narrower sinus and a somewhat higher area; in addition, in Sp. frequens “the greatest width always corresponds to the hinge margin” (ib., 1210), whereas in our species the greatest width always lies below the hinge margin, since the cardinal angles are rounded.

Another close form is Spirifer cabanillus Vern. et Arch. from the Lower Devonian of Spain (1844, 475), which, however, owing to the presence of a ridge in the sinus, is still closer to the variety of our species described below, where a comparison with it is given.

Distribution. Spirifer paucicostus is less widely distributed than the other species of this genus, although its few representatives occur in most outcrops of Medvedev Log. Most often this species occurs in the upper half of the fauna-bearing part of the Medvedev Log sequence.

Holotype — \(\frac{\mathrm{ML}-g_1}{20}\) (dorsal valve); allotype — \(\mathrm{ML}\ g_2\) (ventral valve); paratypes
\[ \frac{\mathrm{ML}-g_3}{22};\quad \frac{\mathrm{ML}-g_3}{19};\quad \frac{\mathrm{ML}-g_8}{28a} \]
(internal mold of a complete shell).

Spirifer paucicostus Khalf., n. var. altaica

Table IV, figs. 7—8

I have only two specimens of this variety, which in all respects resembles the typical form, but possesses in the sinus of the ventral valve a distinct median ridge. Since this is its only difference, I do not consider it necessary to separate this form as an independent species; all the more so because, in the dorsal valves, the variety altaica and the typical form are indistinguishable.

This variety shows the greatest similarity to the Lower Devonian Spirifer cabanillus V. et A. (1844, pl. XV, fig. 6), which differs in having a higher area, a broader and flatter sinus, and also in the presence on the saddle of a longitudinal depression, which is absent in our form.

Holotype — ML—g₈, paratype — ML—g₁₀

Spirifer korovini Khalf.

Table III, figs. 1—6; table IV, fig. 1

1. Spirifer korovini: Khalfin. Materials on the stratigraphy of the Devonian deposits of Altai, p. 18, pl. V, figs. 3, 4.

Specific characterization. The shell is strongly developed in width, of semi-elliptical outline, with the hinge margin corresponding to the long axis of the ellipse.¹)

Adult specimens of this species reach enormous dimensions—up to 15 cm in width. The ratio of width to length ranges from 2.2 (in young individuals) to 4.0 (in adults). The cardinal angles are rounded, owing to which the greatest width lies below the hinge margin, but usually in immediate proximity to it.

The ventral valve is markedly convex; the beak is incurved; the area is moderately developed and has the character of a low triangle, strongly elongated at its base. The sinus begins at the beak, is broad and deep; its bottom is rounded and smooth. On internal molds traces are visible of strong, but not very long, slightly diverging dental plates; the delthyrial plate is absent; a large oval muscle scar is divided by a deep depression and covered with feathery striation; on its sides there are numerous punctate ovarian impressions.

The dorsal valve is less convex than the ventral one. The saddle begins at the beak and very rapidly broadens toward the anterior margin; it is bounded by sharp rectilinear furrows, which give it triangular outlines; the saddle is high, roof-shaped, with a rather sharp crest.

The sculpture consists of a few large, flatly rounded radial folds, separated by likewise rounded but narrower interspaces. On internal molds of the ventral valves they are only occasionally very faintly visible; usually these molds appear smooth. By contrast, on internal molds of the dorsal valves these folds are quite distinct, usually numbering three on each side of the saddle; in large specimens a fourth fold is often faintly indicated; the parts of the valve adjoining the cardinal angles appear smooth on internal molds. The width of the two folds nearest the saddle is only half the width of the saddle near the anterior margin. On some internal molds traces of fine radial striae, preserved along the margins of the shell, are clearly visible; apparently the outer surface of the shell bore fine elements of radial sculpture. Rather numerous and sharp growth marks are also preserved on the internal molds.

¹) In contrast to what we saw in Sp. paucicostus.

Dimensions:

Similarities and differences. The distinctive features of this species are the small number of folds and the very broad roof-shaped saddle; these characters distinguish our species from the Lower Devonian groups Spirifer hercyniae Gieb. and Spirifer kayserianus Clarcke, and also from the Middle Devonian group Spirifer cheehiel kon. Among more closely related forms may be noted: the Lower Devonian Spirifer parana Clarcke (1913, 250), distinguished by acute cardinal angles, a narrower and more rounded saddle, and broader radial folds; representatives of the Lower Devonian Spirifer undulifer Kays. (Scupin 1900, 266), developed in width, which likewise possess a narrower and more rounded saddle and a higher triangular area. The Middle Devonian Spirifer macrothyris Hall (1867, pl. XXX, fig. 16), close in outline and in the character of the saddle, has a more developed area and a considerably greater number of folds.

Distribution. Spirifer korovini is absent only in the very lowest horizons of the Medvedev Log sequence, and then occurs in a small number of specimens through all horizons, reaching mass development only in the upper part of the section.

Holotype: \(\frac{\mathrm{ML}-g_{11}}{22}\) (dorsal valve); allotypes: \(\frac{\mathrm{ML}-g_{12}}{22}\) and \(\frac{\mathrm{ML}-g_{14}}{22}\) (juvenile specimens); \(\frac{\mathrm{ML}-g_{16}}{25}\) (mold of a dorsal valve with traces of radial striation); \(\frac{\mathrm{ML}-g_{27}}{37}\) (molds of ventral valves); \(\frac{\mathrm{ML}-g_{31}}{28}\) and \(\mathrm{ML}-g_{34}\) (molds of complete shells).

Spirifer rarus n. sp.

Plate III, fig. 7.

This species stands in unquestionable closeness to the preceding one—it has the same outlines, metric ratios, and character of plication and saddle. The only difference sharply striking the eye that separates it from Spirifer korovini consists in the larger number of radial folds: on each side of the saddle there are five distinct folds, and a sixth is indicated. Corresponding to their greater number, the folds are less broad, and the intervals between the folds are also narrower; in addition, the folds are sharper and less flat than in the preceding species.

The undoubted genetic closeness of the species described here to the original Sp. korovini compels us to regard this species also as a certain native form, especially since among the spirifers described in the available

literature available to me I do not find an identical form. Especially characteristic of Sp. rarus, as also of Sp. korovini, is a very broad, roof-shaped saddle in combination with a small number of radial folds. These characters readily distinguish Sp. rarus even from the most closely similar forms (such as, for example, Spirifer antarcticus Morr. et Sh.—see Clarke (1913, pl. 18, fig. 10).

Spirifer rarus is a very rare form among the fauna of Medvedev Log: among more than two hundred specimens of various spirifers in my collection of this fauna there are only two dorsal valves of this species.

Holotype—$\dfrac{\text{ML—g}_{36}}{22}$; paratype—ML—g$_{37}$.

Spirifer pseudofallax Khalf.

Table II, figs. 3—9.

1. Spirifer pseudofallax: Khalfin. Materials on the stratigraphy of the Devonian deposits of Altai, p. 18, pl. V, fig. 8.
2. Spirifer paticicostus (pars), ibidem, p. 18, pl. V, fig. 5.

Specific characterization. The shell is rounded in outline, attaining very large dimensions; the ratio of width to length in adult individuals is about 1.5. The hinge margin is long, but somewhat less than the greatest width of the shell. The greatest width passes approximately halfway between the anterior and posterior margins. The lateral and anterior margins are outlined by an evenly convex, smooth curve approaching a circle. Both valves are weakly convex.

The ventral valve has a rather high area of triangular outline, in the middle of which is situated a broad open delthyrium. The beak is slightly incurved, owing to which the area acquires a weakly concave character. In the largest specimens the height of the area reaches 10—11 mm, with the length of the hinge margin exceeding 60 mm. The sinus begins at the very beak; it is narrow and deep, having in transverse section a form close to the Roman V; the floor of the sinus is slightly rounded. On internal molds of ventral valves there are visible, rarely almost parallel but usually diverging at an acute angle, long and rather thin dental plates. They delimit a narrow and long muscular ridge, scarcely projecting above the surface of the remaining part of the internal mold, deeply divided by the sinus; on it a weak fan-shaped striation is sometimes visible.

The weakly convex dorsal valve bears a high, raised, roof-shaped saddle with a sharp or only slightly blunted crest. The saddle begins at the very beak and is bounded by sharp depressions. Its width near the anterior margin is equal to the width of 3—4 adjacent folds. In the posterior part of the saddle there is noticeable the trace of a weak median septum in the form of a thin riblet.

The sculpture consists of rounded radial folds. On the ventral valve they are usually very weakly developed, whereas on the dorsal valve they are quite distinct; I have internal molds of shells of this species in which the ventral valve is smooth, while the dorsal is distinctly folded. In my collection there are impressions of the outer surface of the ventral valve on which folding is not detectable. On internal molds of dorsal valves three folds are clearly distinguishable on each side of the saddle; the fourth folds are usually fairly distinct, and a fifth is sometimes indicated. The folds are rather high, rounded; the spaces between them are narrower. Usually a few sharp growth marks are visible on the specimens.

Dimensions:

Remarks: I know of no species that would be so close to Spirifer pseudofallax as to make comparison necessary. Such Lower Devonian forms as Spirifer decheni Kays., Spirifer fallax Gieb., Spirifer iheringi Kays., and some others have one or another character in common with our species, but possess, in far greater number, characters that readily distinguish them from the form described. The young shells of our species stand closest to Spirifer pseudoviator Scupin from the Lower Devonian of the Eastern Alps; the dorsal valve of this species illustrated by Scupin (1906, Taf. XIV, fig. 14) differs from young specimens of the form described only in its rounded saddle and somewhat sharper plication; the drawings in the text (ib., 290) already reveal greater differences, in particular in the outlines of the shell; it is interesting that in these drawings the plication of the dorsal valve is shown sharper than that of the ventral valve, which, as noted above, is characteristic of all the spirifers from Medvedev Log.

Distribution. This species is distributed in the same way as Sp. korovini, and, like the latter, has a mass development in the upper part of the section.

Holotype — \(\dfrac{\mathrm{ML}-g_{40}}{22}\) (internal mold of a complete shell); allotypes: ML—\(g_{42}\) and ML—\(g_{43}\) (ventral valves, area); ML—\(g_{47}\) and \(\dfrac{\mathrm{ML}-g_{49}}{26_1}\) (young individuals).

Spirifer semicirculus n. sp.

Plate IV, fig. 4.

Specific diagnosis. Shell of large size, strongly developed in width, with a semicircular outline. The greatest width of the shell coincides with the hinge line or lies in immediate proximity to the latter (in those cases where the cardinal angles are slightly rounded). The anterior and lateral margins are outlined by a smooth curve. The convexity of both valves is moderate. The area of the ventral valve is not high, the beak curved. From the beak begins a sinus, gradually widening toward the frontal margin; the sinus is not wide and, apparently, not very deep. The dental plates are short, in large specimens very thick, in smaller ones thin, diverging from the beak at an acute angle. On internal molds they delimit a weakly developed muscular field, deeply divided by the sinus; it bears fan-shaped striation. The saddle of the dorsal valve also begins from the beak and, rapidly widening, reaches a great width at the anterior margin; the saddle is high, roof-shaped, with a slightly blunted crest. On each side of the saddle there are 3–4 very flat and broad radial folds; on internal molds of ventral valves these folds are only faintly indicated or are not distinguishable at all.

Dimensions:

Similarities and differences. This species shows features of similarity with Sp. korovini, but differs from it quite readily. It is brought close to Spirifer korovini by the development of the shell in width (apart from the character of the saddle and the folding, which are generally identical in all our spirifers); however, the outline of the shell in these two species is entirely different: in Sp. korovini the anterior margin on both sides of the saddle continues for a considerable distance almost parallel to the hinge margin, and then, smoothly rounding, passes into the convex lateral margins; in Sp. semicirculus the anterior margin, immediately from the saddle, rises toward the cardinal angles. Therefore in Sp. korovini the lateral parts of the shell are broad, scarcely narrowing toward the cardinal angles, whereas in Sp. semicirculus they have subtriangular outlines and narrow strongly toward the cardinal angles. In addition, in Sp. korovini the valves, especially the ventral one, are more convex, the sinus is broader and deeper, the muscular scar is more developed, and the cardinal angles are more rounded.

From Sp. pseudofallax the present species is readily distinguished by its outlines and by the greater ratio of shell width to length.

Remarks. This species is represented in my collection by a few specimens, which are internal molds of isolated ventral and dorsal valves. These specimens are imperfectly preserved, and therefore some details cannot be established precisely, for example the character of the sinus. Nevertheless, these specimens differ so substantially from all our other spirifers that it proved necessary, on their basis, to establish a new species, the diagnosis of which will apparently be refined and supplemented in the future.

Distribution. This species is considerably less widespread than Sp. korovini or Sp. pseudofallax and has been found only in the upper half of the fauna-bearing part of the section along Medvedev Log.

Holotype—$\dfrac{\text{ML—g 62}}{22}$; paratypes $\dfrac{\text{ML—g 64}}{24}$; $\dfrac{\text{ML—g 66}}{23_1}$

Spirifer cf. assimilis Fuchs

Plate IV, fig. 5.

In my collection there is one dorsal valve $\dfrac{(\text{ML—g 67})}{29}$, which cannot be assigned to any of the species described above. The dimensions of this valve are: length 30 mm, width 40 mm; the outlines are trapezoidal. The hinge margin constitutes the greatest width of the shell; the cardinal angles are pointed. The saddle, beginning from the beak, is bounded by sharp furrows; its width at the anterior margin is 16 mm; the saddle is high, roof-shaped, and its crest was apparently sharp or slightly rounded (because of the deformation of the specimen the character of the crest of the saddle cannot be established precisely). On each side of the saddle there are three distinct and one less noticeable radial folds; the folds are broad, rounded, separated by narrower intervals. The width of the two largest—

the larger ones adjacent to the saddle folds amounts to half the width of the saddle.

The specimen described is apparently a representative of some new species; I refrain from establishing this species because I have only the single specimen described above. This specimen closely recalls some Lower Devonian European spirifers. Most of all it shows similarity to young individuals of Sp. assimilis from the Lower Devonian deposits of the Middle Rhine; this is easily verified by comparing our illustration of the specimen described with fig. 11 on pl. 5 in Fuchs’s work (1915); the difference is the smaller number of folds in our specimen. Adult individuals of Sp. assimilis differ more substantially.

Another close form is Spirifer Jlsae Kays. from the Lower Devonian of the Harz (Kayser, 1878, 167), which likewise differs in a larger number of radial folds and, moreover, in a more convex dorsal valve. The specimen comes from an outcrop in which other spirifers are almost absent (including such common forms as Sp. korovini and Sp. pseudofallax).

Spirifer cf. mischkei Frech.

Pl. IV, fig. 3.

1. Spirifer cf. mischkei: Khalfin. Materials on the stratigraphy of the Devonian deposits of Altai, p. 18, pl. V, fig. 7.

I have two dorsal valves of subrectangular outline, which closely resemble the cited species.

Their dimensions are as follows:

length — 20; 28
width — 31; 50.

The hinge margin is only slightly shorter than the greatest width, which passes through the middle of the shell. The anterior margin is parallel to the hinge margin; the lateral margins are flatly rounded, almost straight. The saddle begins at the umbo, is high, with a strongly rounded top, which distinguishes the specimens described from all the other spirifers of Medvedev Log. On the posterior half of the saddle there is visible, in the form of a thin and weak groove, the trace of an incipient median septum, as in Sp. pseudofallax. On each side of the saddle there are three radial folds; the latter are of the type usual for our spirifers: broad, flat, separated by narrower but likewise rounded interspaces. Growth lines are numerous and sharp.

Of all the spirifers of Medvedev Log described above, this form differs in its outline and rounded saddle. It shows great similarity to Spirifer mischkei Frech.

Spirifer n. sp., cf. Sp. iheringi Kays.

Pl. IV, fig. 6.

In my collection there is one incomplete internal mold of a dorsal valve, presenting a number of sharp distinctive features from our other spirifers. In size, convexity, and outline this dorsal valve is very close to adult individuals of Spirifer pseudofallax, from which it is readily distinguished by the different character of the saddle and sculpture. The saddle of the valve described is moderately high, flat-topped, with vertical sides; it begins at the umbo, is bounded by very sharp depressions; on the posterior half of the saddle there is visible the trace of a thin

septa. The sculpture consists of radial folds, narrower and less rounded than in all the spirifers described above, but the grooves between them are broader and more rounded. On each side of the saddle there are 6 such folds; on the parts of the valve adjacent to the cardinal angles the folds are not noticeable at all. Near the anterior and lateral margins there are several very sharp growth marks. Dimensions of the specimen: length—about 40 mm, width about 76 mm.

The specimen described differs so substantially from all the other species of spirifers from Medvedev Log that it cannot be assigned to any of them. Nor is there, in the literature available to me, any previously described species with which I could identify this specimen. More than others, this specimen recalls Spirifer iheringi Kays. from the Lower Devonian of South America (Clarke, 1913, 243); however, in Kayser’s species the radial folds are much coarser than in our specimen and occupy almost the entire surface of the valve on either side of the saddle, whereas in the Altai form the sectors adjacent to the cardinal angles and devoid of folds are very considerable.

The specimen described (ML—g₇₀) was found in the alluvium of the B. Tikhaya River.

Spiriferidae of Kondratyevskaya Hill.

Genus Delthyris Dalm.

In the deposits of Kondratyevskaya Hill, representatives of this genus alone have been encountered; they are fairly varied, but quantitatively so poorly represented that in our collection they are present, as a rule, as single specimens of internal molds of isolated valves. For this reason an exact determination of our specimens is impossible, and in their names I am forced merely to indicate the nearest of the previously described forms with which our specimens are probably identical.

Among our delthyrids two groups can be distinguished: one of them is represented by four specimens belonging to four different species with unfolded or very weakly folded valves; the molds of the ventral valves show a well-developed septum; the closest analogues are distributed in the European Lower Devonian. The other group, represented by four incomplete impressions, has sharper and more numerous folds and sharp lamellate growth marks; the closest form is the American Delthyris perlamellosa Hall, which I also encountered in the deposits of the Ganin Key. Brief characteristics of the spiriferids found in the deposits of Kondratyevskaya Hill are given below.

Delthyris cf. koegeleri Scup.

Plate IV, fig. 10.

Comp.: Spirifer Koegeleri: Scupin. Zeitschr. deutsch. geol. ges., Bd. 58, S. 294, Taf. XVII, Fig. 14, 15.

The internal mold of the ventral valve is subrhombic in outline, slightly developed in width; the area is high, triangular, the umbo curved. From the very umbo begins a sinus which, at the anterior margin, reaches considerable width and has a V-shaped cross-section. A thin septum falls a little short of half the length of the valve. In addition to the weak folds bounding the sinus, one very faintly expressed fold is discernible on each side of it.

This specimen shows great similarity to Delthyris koegeleri from the Lower Devonian of the Carnic Alps (see synonymy); it differs only in its somewhat broader sinus and, apparently, longer septum.

Specimen dimensions: length, width

Specimen number—$\dfrac{\mathrm{B}_7-1a}{5}$

Delthyris cf. carinthiaca Frech.

Plate IV, fig. 9.

Comp.: Spirifer carinthiacus: Scupin. Zeitschr. deutsch. geol. ges., Bd. 58, S. 295, Taf. XVII, Fig. 5, 13, 16.

An internal mold of a ventral valve similar to the preceding one, but possessing a longer beak (correspondingly a higher area), a deeper sinus bounded by sharper folds, and a noticeable tendency toward the formation of very weak lateral folds. The median septum is thin and long (exceeding half the length of the valve); in the apical part, along its sides, there are (within the sinus) two short dental plates.

Specimen dimensions: length, width

The specimen shows complete similarity to the Carnian representatives of Delthyris carinthiaca (see synonymy).

Specimen number: $\dfrac{\mathrm{B}_7-1b}{5}$

Delthyris cf. robusta Barr.

Comp.: Spirifer robustus: Barrande. Syst. sil., vol. V, pl. 5, fig. 1—4.

An incomplete internal mold of an unfolded dorsal valve; the saddle beginning at the beak is slightly flattened above and has steep sides; in the posterior part of the saddle a trace of a weak median septum is visible. The length of the specimen is not less than 15 mm, the width—28 mm.

The characters available for observation on this extremely imperfect specimen allow one to speak of its great similarity to the Bohemian Delthyris robusta from stage F—only the saddle in our specimen is somewhat narrower.

Specimen number—$\dfrac{\mathrm{B}_7-2}{3}$

Delthyris cf. jaschei A. Roem.

Plate IV, fig. 11.

Comp.: Spirifer Jaschei. Kayser. Fauna ältest. Dev.—Abl. usw., S. 176.

A small internal mold, developed in width, of a dorsal valve with a long hinge margin and rounded cardinal angles. The high saddle, with a rounded crest, begins at the beak and is bounded by rounded but distinct furrows; the width of the saddle near the anterior margin is about 0.7 of the valve width. On each side of the saddle there are two distinct rounded folds. A few sharp growth marks are noticeable.

Dimensions: length, width

Specimen number—$\dfrac{\mathrm{B}_7-3}{5}$

Delthyris perlamellosa Hall, n. var. altaica.

Plate IV, figs. 12, 13.

Three incomplete impressions of the external surface of ventral valves and one impression of the area.

The ventral valve is strongly convex, with a long, curved beak. The hinge margin corresponds to the greatest width of the shell; the cardinal angles are pointed. The area is high, triangular, concave; the delthyrium in the upper part is closed by two deltidial plates; the boundary between them is marked by a distinct little ridge. The sinus begins at the beak, is broad and deep, with a rounded bottom. It is bounded by two very sharp folds, besides which there are, on each side of the sinus, up to 7 radial folds. The radial folds are sharp, subangular; the two marginal folds are very weakly expressed. The width of the sinus is equal to the width of four adjacent ribs. The entire surface of the valve is covered with numerous, dense, very sharp lamellar growth markings.

Dimensions of the most complete specimen:

length — 20; width — 42.

Our specimens show great similarity to typical representatives of Delthyris perlamellosa, but differ in having finer and more numerous radial folds: in the American form their number ranges from 4 to 6–7, whereas in our specimens it is 8 on each side of the sinus. Having at my disposal very insufficient material, I confine myself for the present to including our specimens in Hall’s species as a local variety.

Golotip: $\dfrac{B_7 - 4}{5}$; paratypes: $B_7 - 5$; $\dfrac{B_7 - 6}{6}$; $B_7 - 7$

CONCLUSION

The Lower Devonian fauna of the Altai is, for the most part, endemic, and for this reason an exact solution to the question of the age of the corresponding deposits cannot be obtained by using for these purposes only any single group of this fauna. However, the family Spiriferidae is a component of this fauna that is of considerable interest in this respect as well.

A sufficiently detailed analysis of the fauna of Kondrat’evskaya Sopka and Medvedev Log was presented in my report at the First Conference on the Study of the Productive Forces of Siberia (1940). In brief, the conclusions of this analysis amount to the following:

1. In composition, the fauna of Medvedev Log and the fauna of Kondrat’evskaya Sopka differ greatly not only with respect to species units (the common species are very few), but also with respect to larger taxonomic units.

2. In the composition of the fauna the influence of the European and American faunas is evident; the influence of the European fauna is more significant and more direct, but nevertheless the connection of the Altai Lower Devonian basin with the seas of Europe and America was limited, owing to which a fauna with a decisive predominance of endemic forms developed in this basin.

1. The fauna of Medvedev Log is Upper Koblenzian; the fauna of Kondrat’evskaya Sopka is somewhat older.

2. The deposits of Medvedev Log and Kondrat’evskaya Sopka are facially distinct, the former being more shallow-water; the fauna of these deposits, while remaining largely endemic and representing a peculiar type of mixture of European, native, and American elements, in its facial nature (and partly also in its composition) approaches the mixed Rhenish-Bohemian faunas of Europe; at the same time the fauna of Kondrat’evskaya Sopka is similar to the fauna of the Erbsloch graywacke, while the fauna of Medvedev Log approaches the normal Rhenish type.

3. The facial and stratigraphic differences between the deposits of Kondrat’evskaya Sopka and Medvedev Log are insufficient to explain the profound differences in the composition of the fauna of these deposits; the younger fauna of Medvedev Log, in its main body, shows no genetic connection with the fauna of Kondrat’evskaya Sopka, i.e., it is not a product of the evolution of this latter fauna. This is explained by the fact that the formation of the Kondrat’evskaya Sopka sequence and the Medvedev Log sequence was separated by a temporary drying-up of the Lower Devonian basin of Northern Altai, in which the manifestation of the Kuyagan phase of tectogenesis is expressed; the sea that returned within the limits of Northern Altai at the very end of the Lower Devonian was populated by an immigrant fauna substantially different from the fauna of Kondrat’evskaya Sopka.

Turning to the spiriferids described in this article, we can also establish within this family a mixture of European and American elements: Eospirifer pseudotogatus and the delthyrids of Kondrat’evskaya Sopka have a quite distinctly expressed European type, but alongside them our fauna contains such a typical North American species as Delthyris perlamellosa.

All our spiriferids, without exception, with greater or lesser certainty indicate a Lower Devonian age for the fauna. This indication is especially definite for the fauna of the Ganyin key: Delthyris perlamellosa characterizes the lower horizons of the Eodevonian in North America; the closest European analogues of our Eospirifer pseudotogatus—namely, Spirifer togatus, Sp. secans—are likewise distributed in the very lowest horizons of the Devonian (partly in the Upper Silurian), in the Rhenish Slate Mountains, the Harz, and Bohemia. In the composition of the fauna of the Ganyin key there are altogether absent those elements tending toward Koblenzian forms which are established in the fauna of Kondrat’evskaya Sopka and, to an even greater degree, in the fauna of Medvedev Log. Thus, it may be accepted that in the deposits of the Ganyin key we have in Altai the very lowest horizons of the Lower Devonian, whereas the deposits of Kondrat’evskaya Sopka and Medvedev Log give us two subsequent formations of this division of the Devonian system. In other words, within Northern Altai, at least a three-member division of the Lower Devonian is established.

The spiriferids of Kondrat’evskaya Sopka, because of the approximate character of most of the determinations, cannot serve as a wholly reliable basis for geological conclusions, but their Lower Devonian age and Western European type are beyond doubt.

Finally, the spirifers of Medvedev Log prove to stand apart when compared with the spiriferids of Kondrat’evskaya Sopka and the Ganyin key; this is expressed not only in the species composition, but even more clearly in the fact that the spirifers of Medvedev Log have a sharply expressed native character. It seems to me beyond doubt that in them we have a completely isolated association of organisms, characterizing (among other native groups) the peculiar Lower Devonian fauna of Altai and having no genetically close groups among the spiriferids of Europe and America.

References Cited

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11. Fuchs. A.—Hunsrückschief. u. Unterkoblenzschicht. am Mittelrhein. Abh. pr. geol. L.—A., N. F., Ht. 79.

12. Hall, J.—Palaeont. of N. U., vol. III.

13. Hall, J.—Palaeont. of N. U., vol. IV.

14. Hall, J.—and J. Clarcke. Palaeont. of N. U., vol. VIII, pt. II.

15. Kayser. E.—Fauna d. alt. Devon—Abl. d. Harzes. Abh. geol. Specialkarte, Bd. II.

16. Kozlowski. R.—Brachiop. gothland. de la Podolie Polonaise. Polaeont. Polonica, t. I.

17. Meek, F. B. and A. H. Worthen.—Palaeontology of Illinois. Geol. Surv. of Illinois, vol. III.

18. Paeckelmann, W.—Beitr. Z. Kenntn. d. Devons am Bosporus. Abh. pr. geol. L.—A N. F., Ht. 98.

19. Schuchert, Ch.—Synops. of Americ. Foss. Brachiopoda. Bull. U. S. geol. Surv., No. 87.

20. Schuchert, Ch. and T. Maynard. Brachiopoda. Maryl. geol. Surv. Lower Devonian.

21. Schuchert, Ch. and C. Le Vene—Brachiopoda. Fossilium Catalogus.

22. Scupin, H.—Spiriferen Deutsch. Pal. Abh. V. Dames und Koken, Bd. VIII, Ht. III.

23. Scupin, H.—Devon d. Ostalpen. IV. Fauna d. dev. Riffkalkes. II. Brach. Zeitschr. deutsch. geol. Ges., Bd. 58.

24. Tansey, V. O.—Fauna of the Bailey Is. In Branson’s “The Devonian of Missouri”

25. Verneuil et Archiac—Notes sur l. foss. du terr. paléozoïque d. Asturies. Bull Soc. Géol. France, sér. 2, vol. II.

Explanations of Plates

Plate I

Fauna of the Gavina Key

Fig. 1. Eospirifer pseudotogatus n. sp. Holotype.

Fig. 1. Idem. Internal mold of the dorsal valve.

Figs. 3—4. Idem. Internal mold and impression of the ventral valve; dental plates, muscle area; sculpture.

Figs. 5—6. Idem. Two internal molds of ventral valves in the gerontic stage; structure of the dental plates, character of the muscle swelling, impression of the areas.

Fig. 7. Idem. Plasticine cast from the impression of the ventral area.

Fig. 8. Idem. Plasticine cast from the impression of the dorsal area of the specimen illustrated in Fig. 2.

Fig. 9. Delthyris perlamellosa Hall. Internal mold of a ventral valve with the beak cut off: dental plates and septa.

Figs. 10—11. Idem. Internal molds of ventral valves (Fig. 10—enlarged).

Plate II

Fauna of the Gavina Key.

Figs. 1—2. Delthyris perlamellosa Hall. Impression and internal mold of the dorsal valve; character of the sculpture, structure of the dorsal area; enlarged.

Fauna of Medvedev Log.

Fig. 3. Spirifer pseudofallax Khalf. Internal mold of the dorsal valve of a juvenile individual.

Fig. 4. Idem. Character of the saddle.

Figs. 5—6. Idem. Internal mold of the shell, holotype; different expression of the radial sculpture on the ventral and dorsal valves.

Figs. 7–8. Idem. Ventral valve; character of the sinus and areas.
Fig. 9. Idem. Internal mold of the ventral valve; character of the dental plates and muscular callus; weakly expressed radial plication.

Table III.

Fauna of Medvedev Log.

Figs. 1–4. Spirifer korovini Khalf. Four internal molds of dorsal valves of individuals of different ages; outlines, character of the saddle, distinct radial plication; fig. 3—holotype.
Figs. 5–6. Idem. Internal molds of ventral valves; character of the dental plates and muscular callus; absence of radial folds; character of the sinus.
Fig. 7. Spirifer rarus n. sp. Holotype.
Fig. 8. Spirifer paucicostus Khalf. Internal mold of the dorsal valve, holotype.

Table IV.

Fauna of Medvedev Log.

Fig. 1. Spirifer korovini Khalf. Internal molds of three ventral valves.
Fig. 2. Spirifer paucicostus Khalf. Ventral valve in profile.
Fig. 3. Spirifer cf. mischkei Frech.
Fig. 4. Spirifer semicirculus n. sp. Holotype.
Fig. 5. Spirifer cf. assimilis Fuchs.
Fig. 6. Spirifer cf. iberingi Kays.
Figs. 7–8. Spirifer paucicostus Khalf. n. var. mesoloba.

Fauna of Kondrat’evskaya Hill.

Fig. 9. Delthyris cf. carinthiaca Frech.
Fig. 10. Delthyris cf. koegelerei Scup.
Fig. 11. Delthyris cf. Jaschei Roem.
Fig. 12. Delthyris perlamellosa Hall, n. var. altaica; plate impression with imprint of the ventral area—character of the delthyrium.
Fig. 13. Idem. Plate impression with imprint of the ventral valve; numerous radial folds.

Note: all photographs, except where specifically stated above, are natural size.

EXPLANATIONS OF FIGURES IN THE TEXT

Fig. 1. Spirifer pseudotogatus n. sp. Ventral area, delthyrium, dental plates.
Fig. 2. Idem. Ventral muscular field (diagram): ad—adductors, d—diductors, adj—adjustors.
Fig. 3. Idem. Dorsal area: a—notothyrium, b—socket walls, c—traces of dental sockets.
Fig. 4. Delthyris perlamellosa Hall. Natural apical section of the ventral valve (specimen—$\dfrac{\mathrm{KG}-N_2}{14}$): a—dental plates, b—septa.
Fig. 5. Idem. Copy of a drawing from the monograph of Hall and Clark (1894, pl. 25, fig. 13): b—dental sockets, c—spondylium, j—“cardinal process” (notothyrial imprints of the diductors).
Fig. 6. Idem. Structure of the dorsal area (specimen $\dfrac{\mathrm{KG}-N_3}{14}$): a—notothyrial imprints of the diductors, b—traces of dental sockets, c—bases of the spondylium, d—reduced cardinal process.

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