QUESTIONS OF THE GEOLOGY OF KUZBASS, 2

PROCEEDINGS OF THE TOMSK POLYTECHNIC INSTITUTE
OF THE ORDER OF THE RED BANNER OF LABOR named after S. M. KIROV, vol. 99, 1959

BIVALVE MOLLUSKS OF THE INTERMEDIATE SUBFORMATION OF THE KEMEROVO REGION OF KUZBASS

R. N. BENEDIKTOVA

In the faunistic characterization of the section of the coal-bearing deposits of Kuzbass there has until now been a large gap concerning the Intermediate and Ishanovo subformations, although both below them (in the Lower Balakhonka suite) and above them (in the Usyat subformation and in the Kolchugino series) abundant fauna is present. Until now only isolated finds of pelecypods were known from the base of the Intermediate subformation, belonging to the group Mrassiella magniforma Rag. and still quite analogous to the mrassiellas of the Alykaevo subformation [6]. In addition, in the Kemerovo region, in the Ishanovo subformation, two specimens of pelecypods were found [4; 5]: Naiadites skoki Fedotov and Yavorskielia skoki (Fed.). These are all the data at our disposal on the fauna of the Intermediate and Ishanovo subformations. This gap in our knowledge is especially noticeable because, until now, between the rich and varied fauna of the Alykaevo subformation and the equally abundant fauna of the Usyat subformation, we know of no transitional associations, and these faunas are entirely different from one another [6].

The paleontological materials collected by the Kemerovo geological-survey party of the trust “Kuzbassuglegeologiya” in 1955 and 1956 in one of the sectors of the Kemerovo coal region (namely, in the Butovka-Western sector) proved to be entirely unexpected. Here, in this sector, a fairly numerous fauna of pelecypods was found for the first time in the deposits of the Intermediate subformation; moreover, it includes forms with a distinctly expressed Alykaevo aspect (although it consists of new species). Especially unexpected was the presence of the genera Cirravus Chernyshev and Kinerkaella Khalfin, which in all regions of Kuzbass disappear at the top of the Alykaevo subformation, marking the boundary between the Lower and Upper Balakhonka suites, whereas here they continue to exist in the Intermediate subformation.

But alongside these Alykaevo elements, in the Intermediate subformation of the Butovka-Western sector there are also present (and quantitatively predominate) specific species of pelecypods, chiefly anthraconautids.

In connection with the foregoing, the question arises: why was the fauna in the Intermediate subformation practically not encountered by anyone in any region, whereas in the Butovka-Western sector it proved to be fairly abundant and diverse? Is this sector a fortunate exception, or were the searches for fauna in the Intermediate and Ishanovo subformations simply not sufficiently thorough until now? The latter supposition seems unlikely, since the pelecypods now found in the Intermediate

subformation, are numerous, and have large dimensions, i.e., they should not have escaped attention even during surface collecting.

Another serious question also arises: has the position of the section of the Butovka-Western area in the general stratigraphic scheme of Kuzbass been correctly determined? The fact is that this area is tectonically isolated. The staff of the Kemerovo party of the trust “Kuzbassuglegeologiya” assign the entire section of this area to the intermediate subformation and to the lower part of the Ishanovo subformation and, accordingly, name the coal seams of this section beginning with the Stepanovo seam downward¹. But M. D. Parfenova, who studied the flora from this section, indicates that in its lower part, up to the seam that is correlated with the Double-Intermediate seam, Alykaevo plants are still distributed, and only at the level of this seam do forms typical of the intermediate subformation appear (in particular, leaves of the bud-scale type—the genus Lepeophyllum Zalessky, etc.).

Consequently, on the basis of the flora, the boundary between the Alykaevo and intermediate subformations should be drawn along this seam (which in that case would correspond not to the Double-Intermediate but to the Stepanovo seam). But even in this case the principal part of the fauna described below comes from the intermediate subformation.

It remains to assume that in this region of Kuzbass, during the formation of the intermediate and Ishanovo subformations, conditions existed that were not the same as in other regions. The character of the fauna permits us to say that at times the same conditions arose here as existed in the Mazurovo and Alykaevo ages, when the basins present in the Kuznetsk Basin were influenced by the sea and were brackish. As a consequence of this, brackish-water pelecypods and barnacles (the genus Cirratus) sporadically appear here in the deposits of the intermediate subformation, whereas in all other regions of Kuzbass, by the end of the Alykaevo age, conditions had changed in such a way that the Alykaevo fauna could no longer exist.

This supposition is confirmed by an interesting find made in his time by V. I. Skok: in deposits of the Ishanovo subformation of the Kemerovo district, this researcher found a shell of the semimarine genus Yavorskjella Khalfin, with characteristic radial ribbing, which is not encountered anywhere else in other regions of Kuzbass (but is abundantly present in the Gorlovka Basin). D. M. Fedotov [5] emphasized the marine aspect of this form.

In general, the fauna of the intermediate subformation differs from the Alykaevo fauna, apart from its specific species composition, by the absence of the genera diagnostic for the Lower Balakhonka subformation: Orthonaiadites Khalfin and Angarodon Ragozin.

It is readily distinguished from the Usyatka (Late Balakhonka) fauna: on the one hand, it lacks the gigantic anthraconautids and mrassellids that are so characteristic of the Usyatka subformation, and, on the other hand, it also lacks the very small pelecypods of the group Abiella ussovi Ragozin and the genus Dictys Khalfin.

Since the fauna of the intermediate subformation has not been known until now, we cannot make any stratigraphic correlations on its basis. But it is possible to characterize the change of fauna through the section of the Butovka-Western area. In doing so, we shall tie the fauna to the coal seams with the names assigned to them by the Kemerovo party of the trust “Kuzbassuglegeologiya,” although, as noted above, the ques—

The question of the position of the boundary between the Alykaevskaya and Intermediate subformations in the section of the Butovskii-Zapadnyi area requires additional discussion, and, possibly, the bed called the Double-Intermediate in fact corresponds to the Stepanovskii bed. Below this bed occur the usual Alykaevskaya pelecypods, in particular, Kinerkaella cf. balakhonskiensis (Ragozin) (Table 1, Fig. 11) and Mrassiella magniforma Ragozin.

Stratigraphically higher, two layers containing numerous remains of pelecypods are noted: one of them lies in the roof of the Double-Intermediate bed, the other—10–17 m above the Abramovskii bed. In the first of these there are rather many incomplete and indeterminate impressions of shells from the genera Mrassiella Ragozin and Anthraconauta Pruvost; those forms that could be identified proved to be new (Mrassiella kemeroviensis sp. n., Mrassiella sp. n. cf. M. concinna Khal., Anthraconauta klepovi sp. n.).

The mixture of brackish-water Mrassiella and freshwater Anthraconauta indicates that the pelecypods of this layer lived in a very strongly freshened basin.

The second faunistic layer (above the Abramovskii bed) contains an entirely different pelecypod fauna. It consists of Anthraconauta, moreover of new species (A. butovi, A. obliquilingualis, A. mrassiellaeformis, A. pseudolongissima, A. cf. sibirica); this fauna apparently already inhabited a completely freshwater body.

Comparison of the pelecypods of these two layers shows that the character of the basins in this region during the formation of the deposits of the Intermediate subformation changed: they were now fresh, now brackish. These fluctuations occurred repeatedly, since brackish-water fauna appears sporadically in layers at different levels. For example, the species Mrassiella umbonata sp. n. was found between the Pyzhinskii and Kutashevskii beds; representatives of the genus Cirravus appear in different layers up to the Nadabramovskii bed, where one specimen of the species Kinerkaella oblonga (Ragozin) was found together with them.

Finds of remains of semimarine organisms in the Intermediate and Ishanovskaya subformations make it possible to say that the northern regions of the Kuznetsk Basin, throughout the entire time of formation of the deposits of the Balakhonka series, experienced, though not continuously, the influence of marine and semimarine basins situated somewhere within the Kolyvan-Tomsk zone. But only twice, during the deposition of the Alykaevskaya subformation and the lower part of the Kuznetsk suite, did brackish waters spread over the entire basin, and with them the fauna that inhabited them: the Alykaevskaya and Early Kuznetsk faunas [6]. During the formation of the deposits of the Ostrogskaya and Upper Balakhonka suites, however, marine and semimarine waters appeared only occasionally and for a short time in the northern part of the basin.

M. F. Neuburg [2] indicates that, beginning at the boundary between the Alykaevskaya and Intermediate subformations, the composition of the flora changes: leaves of the bud-scale type appear, which points to sharp seasonal fluctuations of climate. One might suppose that the rapid disappearance of the Alykaevskaya fauna at the lower boundary of the Intermediate subformation is connected with this change of climate, that the low temperature of cold seasons acted fatally on this fauna, which had previously developed under conditions of an equable climate. But the composition of the fauna and flora of the Intermediate subformation of the Butovskii-Zapadnyi area shows that this is not so: among the plant remains there are many bud leaves, while the pelecypods and conchostracans show no signs of suppression. Apparently, the decisive influence on the disappearance in Kuzbass of the Alykaevskaya and Early Kuznetsk—

of the Donets fauna; perhaps the freshening of the basins in which it lived, possibly in combination with some other factors still unknown to us.

The fauna described below is kept in the Paleontological Cabinet of the Tomsk Polytechnic Institute (TPI) named after S. M. Kirov.

Description of species

Anthraconauta butovi sp. n.

Plate 1, fig. 8.

Holotype. Collection of TPI, museum number 281. Kuznetsk Basin, Kemerovo district, Intermediate Subformation.

Description. Shell of large size, developed in length, on the whole slightly widening backward; hinge margin straight, constituting $^3/_5$ of the greatest length of the shell; it joins the anterior margin smoothly, and with the posterior one forms a distinct angle of about 150°. The anterior end is short, low, and passes smoothly and gradually into the evenly convex ventral margin. The posterior margin is very slightly convex, twice as high as the anterior. The lower posterior end is drawn out backward. The ventral and hinge margins are almost parallel for some distance; only in its anterior half does the ventral margin begin to rise noticeably upward.

The umbones are very strongly displaced toward the anterior margin—lying from it at a distance of only $^1/_7$ of the total length of the shell.

The greatest height passes through the upper posterior angle, is somewhat less than half the greatest length of the shell, and is one and a half times greater than the height passing through the umbo. The angle between the hinge line and the direction of the main diagonal is less than 30°.

The sculpture of the outer surface of the shell is represented by dense concentric lines, very fine and numerous, of equal width over the entire surface of the valve.

The rather coarse marks of growth interruptions of the shell are few (about ten) and widely spaced.

Dimensions: length—34 mm; height—15 mm; (holotype).

Comparison. The form described shows some resemblance to the Late Balakhonian species Anthraconauta lanceolata Ragozin [6, p. 71, pl. VI, fig. 12], but differs in a shorter hinge margin, a larger upper posterior angle, a more drawn-out lower posterior end, and more parallel hinge and ventral margins. Anthraconauta longa (Rag.) [6, p. 44] differs in a more convex ventral margin, a straight or even concave posterior margin, and a narrow lower posterior end.

Occurrence: 18 m above the Abramovka seam.

Anthraconauta obliquilingualis sp. n.

Plate 1, fig. 9.

Holotype. Collection of TPI, museum number 321. Kuznetsk Basin, Kemerovo district, Intermediate Subformation.

Description. Shell of large size, with very characteristic obliquely tongue-shaped outlines, developed along the main diagonal. The hinge margin is straight, very short: less than half the length of the shell. The angle between the hinge margin and the direction of the main diagonal is approximately 35°. The anterior end is low and short. The anteroventral margin is outlined by a barely convex curve. The posterior margin for a considerable distance is parallel to the ventral margin: both run at the same angle (about 160°) to the hinge margin. The lower posterior end is very long (constituting half the shell), broad, with parallel—

with parallel margins, which smoothly meet along a broad rounding of the lower-posterior margin. The greatest height equals half the greatest length of the shell. The umbo is somewhat displaced toward the anterior margin.

The sculpture is represented by numerous dense concentric lines.

Dimensions: length — 35.5 mm, height — 18.5 mm; (holotype).

Comparisons. The very characteristic obliquely lingulate outlines of the shell distinguish our form from those described in the literature.

Locality: 17 m above the Abramovo seam.

Anthraconauta (?) mrassiellaeformis sp. n.

Table 1, figs. 5a, b.

Holotype: Collection of TPI, museum number 169-v, Kuznetsk Basin, Kemerovo District, intermediate subformation.

Description. A large shell of obliquely elliptical outline. The hinge margin is straight, short (less than half the length of the shell), and very gradually passes into the anterior and posterior margins. The umbones are only slightly removed from the anterior margin relative to the total length of the shell, but on the short upper margin they appear noticeably closer to its middle. The angle between the hinge margin and the direction of the main diagonal is 40–50°. The anterior-ventral margin is long, strongly convex; the posterior margin is straight almost throughout its entire extent, owing to which the point of inflection is clearly visible where it meets the rounding of the drawn-out lower-posterior end. The greatest height of the shell is approximately \(3/5\) of its length. The sculpture is represented by very fine, but sharp, dense, regular concentric lines.

Dimensions: length — 29 mm; height — 18 mm.

Comparisons. The collection contains one specimen in the form of a steinkern and impression of the right valve. The unusual outlines of the shell (a very short hinge margin, rounded upper angles, a straight posterior margin), in combination with a very dense concentric sculpture, distinguish this species from all known ones. The general appearance of the shell is somewhat unusual for representatives of the genus Anthraconauta Pruvost.

Locality: 10 m above the Abramovo seam.

Anthraconauta klepovi sp. n.

Table 1, fig. 3.

1. Anthraconauta sp. (cf. Anthraconauta ampla Khalf.) Benediktova. The first find of the Alikaevo fauna outside Kuzbass, p. 34.

Holotype. Collection of TPI, museum number 191. Kuznetsk Basin, Kemerovo District, intermediate subformation.

Description. A shell of medium size, rounded-triangular in outline, strongly widening posteriorly. The hinge margin is straight, equal to approximately \(2/3\) of the length of the shell. The anterior margin is moderately high, short, outlined by a rather steep curve smoothly passing into the ventral margin. The latter is convex throughout its entire extent, directed at an acute angle to the hinge margin. The lower-posterior end is short, broadly rounded. The posterior margin is evenly convex, meeting the hinge line through a strongly rounded angle equal to approximately 120–130°. The umbo is well developed, somewhat bent forward, situated at the end of the hinge line, and strongly drawn toward the anterior margin. The greatest height of the shell passes through the upper posterior angle and equals approximately \(2/3\) of the greatest length of the shell.

The sculpture is represented by very fine, at times indistinct concentric lines, alongside which rather numerous coarser lines and fairly flat ribs occur.

Dimensions: length—23 mm; height—15 mm; (holotype).

Comparisons. The species described shows great similarity to Anthraconauta ampla Khalf. from the Erunakovskaya Formation of Kuzbass [7, p. 121]; the distinction of our species consists in the larger size of the posterior angle and in the greater distance of the umbo from the anterior margin: at equal dimensions, in Anthraconauta ampla the umbones are removed from the anterior margin by a distance half as great as in Anthraconauta klerovi. Given the great difference in stratigraphic position, it seems necessary to assign the forms being compared to different species.

A completely analogous specimen was found among the pelecypods of the Kainaminskoye deposit in Kazakhstan, in association with Zalykaev species of the genera Mrassiella Rag. and Augea Khalf. (see synonymy).

Occurrence: Dvoinoi-intermediate seam.

Anthraconauta tenuistriata sp. n.

Plate 1, figs. 1, 2.

Holotype. Collection of the TPI, museum number 169-6. Kuznetsk Basin, Kemerovo district, Intermediate Subformation.

Description. Shell of rather large size, rounded-trapezoidal in outline, noticeably widening posteriorly, elongated. Hinge margin straight, slightly more than half the length of the shell, forming a very acute angle with the direction of the ventral margin. Umbones removed from the anterior margin by a distance of \(1/5\) of the shell length. Anterior end short and rather high, outlined by a curve that passes smoothly into the ventral margin. The latter is uniformly convex throughout its entire extent. Posterior margin is also outlined by an evenly convex line. The angle between the posterior and hinge margins is strongly rounded; in general, the posterior margin is directed at an angle of 130–140° to the hinge margin. The greatest height passes through the upper posterior angle and amounts to more than half the shell length.

The sculpture is represented by fine, but distinct, dense, regular concentric lines.

Dimensions:

Comparisons. In its sculpture this form recalls Anthraconauta sibirica (Rag.), but it is easily distinguished by the entirely different outline of the shell.

Occurrence: 10 m above the Abramovskoye seam.

Anthraconauta pseudolongissima sp. n.

Plate 1, figs. 6 a, b.

Holotype: Collection of the TPI, museum number 157. Kuznetsk Basin, Kemerovo district, Intermediate Subformation.

Description. Shell large, strongly oblique, narrow, elongated. Hinge margin straight, less than half the shell length. The angle between the hinge margin and the main diagonal is approximately 20°. Anterior end low. Anterior-ventral margin outlined by a weakly convex curve. Lower posterior end drawn out backward and somewhat downward. The angle between the posterior and hinge margins is obtuse, rounded (about 150°). The greatest height is almost \(2/5\) of the greatest shell length. Umbones are strongly brought close to the anterior margin of the shell.

The sculpture is represented by fine, faint concentric lines, evenly and densely distributed over the entire surface of the shell.

Dimensions: length—47 mm; height—20 mm.

Comparisons. The collection contains one specimen, represented by a mold and an external impression of the right valve. In outline, the form described is very similar to Anthraconauta longissima Khalfin [6, p. 75] from the Usyatka Subformation. It differs in having finer growth lines and in the absence of ribbing on the diagonal elevation.

Occurrence: 17 m above the Abramovsky seam.

Anthraconauta cf. sibirica (Ragozin)

Plate 1, fig. 7.

Description. The shell is fairly large, elliptical in outline. The hinge margin is weakly convex and joins the anterior and posterior margins quite smoothly, without forming any noticeable angles. The umbones are strongly shifted toward the anterior margin.

The angle between the hinge margin and the direction of the main diagonal is 35°.

The greatest height of the shell exceeds half its length. The sculpture is represented by thin, sharp, dense concentric lines.

Dimensions: length—35 mm; height—20 mm; specimen no. 169-a.

Comparisons. In shell outline and characteristic sculpture, the form described shows an exceptional similarity to the species Anthraconauta sibirica (Rag.), which is distributed in the uppermost parts of the Usyatka Subformation and in the lower parts of the Kuznetsk Formation. The occurrence of this species in the Intermediate Subformation is unlikely. Therefore this similarity should, presumably, be regarded as convergent.

Occurrence: 10 m above the Abramovsky seam.

Kinerkaella cf. balakhonskiensis Khalfin.

Plate 1, figs. 11 a, c.

Description. The shell is rounded-rhomboidal in outline, somewhat widening posteriorly. The hinge margin is straight, equal to approximately 3/4 of the shell length; it joins the anterior and posterior margins through rounded angles. The umbo is high, directed forward, shifted toward the anterior margin. The latter is outlined by a rather steep arc and passes imperceptibly into the ventral margin. The lower posterior angle is broadly rounded. The posterior margin is high, straightened in the middle part. The angle between the hinge margin and the direction of the main diagonal is approximately 45°. The greatest height passes through the upper posterior angle and is about 3/4 of the shell length.

The sculpture is represented by thin, not sharp, concentric growth lines. In addition, here and there in the umbo one can observe the finest radial ribbing, which is generally poorly preserved.

Dimensions: length—7 mm; height—5 mm; specimen no. 164.

Comparisons. The collection contains an almost complete mold and incomplete impressions of the external surface of the valves. In outline and sculpture these specimens show no differences from Kinerkaella balakhonskiensis Khalf. from the Lower Balakhonka Formation.

Occurrence: 100 m below the Dvoynoy-Promezhutochny seam (Aldykaevo Subformation?).

Kinerkaella oblonga (Ragozin).

Plate 1, fig. 10.

1. Mrassiella oblonga Ragozin. Pelecypods of the Balakhonka Formation of Kuzbass, pp. 59–60, pl. 1, figs. 7, 9.

1. Mrassiella oblonga Fedotov. Pelecypods from the coal-bearing deposits of predominantly industrial districts of the Kuznetsk Basin, p. 220, pl. 1, figs. 1, 2, 6, 7.

Description. The shell is of medium size, moderately convex; along the main diagonal of the shell there passes a keel-like elevation, from which the surface of the valve descends gently toward the anteroventral margin and steeply toward the hinge margin; near the upper posterior angle the valve is almost flat. The hinge margin is straight; its length is more than half the length of the shell. The beak is well expressed, large, strongly shifted toward the anterior margin, and somewhat inclined forward. The hinge margin joins the anterior margin smoothly; with the posterior margin it forms a more clearly expressed angle, equal to 130°. The anterior margin projects forward, is markedly convex, and merges with the ventral margin imperceptibly, gradually. The posterior margin is weakly convex. The greatest height of the shell passes through the upper posterior angle and amounts to 3/4 of its length.

The angle between the hinge margin and the direction of the main diagonal is about 30°.

The sculpture of the outer surface of the shell is represented by dense, numerous, fine concentric growth lines; on the nucleus, in addition, the finest but distinct dense radial striae are visible.

Dimensions: length — 20 mm; height — 12 mm; specimen No. 307.

Comparisons. We have only one internal mold of the left valve of this species. In the general form of the shell, the presence of a keel-like elevation along the main diagonal, and the character of the radial striation, the specimen described shows complete similarity to the species oblonga, which should be assigned to the genus Kinerkaella Khalfin.

From the specimens described and figured by L. A. Ragozin (see synonymy), our specimen differs only in having a somewhat larger upper posterior angle. As for the specimens of D. M. Fedotov, judging from the description, they possess a somewhat shorter hinge margin (less than half the length of the shell; it should be noted, incidentally, that this cannot be said from the photographs given in D. M. Fedotov’s work).

Distribution. Kinerkaella oblonga is reported from deposits of the Alykaevskaya Subformation in a number of districts of Kuzbass; in the Anzhero district this species was encountered in deposits assigned to the “Alykaevsko-intermediate unit” [5, p. 222].

Locality: 5 m below the Nadabramovsky 1 seam.

Mrassiella kemeroviensis sp. n.

Pl. 1, figs. 14 a, b; 15 a, b.

Holotype. Collection of the TPI, museum number 259. Kuznetsk Basin, Kemerovo district; Intermediate Subformation.

Description. The shell is of medium or large size, elliptical in outline; the main diagonal serves as the long axis of the ellipse. The hinge margin is very short, smoothly connected with the anterior and posterior margins through broadly rounded angles. The beaks occupy a subcentral position on it. The angle between the hinge margin and the direction of the main diagonal is 60–70°. The anteroventral margin is outlined by a gentle, smoothly convex curve. The posterior margin is also outlined by an evenly convex curve. The height and length of the shell are almost equal to one another. The greatest dimension is the long axis of the ellipse (almost coinciding with the main diagonal); the length of the shell is 3/4 of the long axis, and the short axis of the ellipse is somewhat longer than half the long axis. The maximum convexity of the valves passes along the diagonal elevation.

The sculpture is represented by concentric, rather coarse ridges and lines.

Dimensions:

Comparisons. The very short hinge margin with broadly rounded auricles, together with the uniformly convex anterior-ventral and posterior margins, give the shell of this species very characteristic elliptical outlines, which distinguish it from most species of the genus Mrassiella. In the character of the shell outline, comparison is possible only with the species Mrassiella ovata Khalf. [6, p. 39] from the Alykaevo Subformation of the Anzhero district; Mrassiella kemeroviensis is readily distinguished from this species by its narrower shell: in our species the minor axis of the ellipse is slightly greater than half the major axis, whereas in Mrassiella ovata it is somewhat less than the latter; in our species the length of the shell is about 3/4 of the length of the main diagonal, whereas in Mrassiella ovata these measurements are almost equal. Therefore, as a whole, the shell in Mrassiella ovata appears considerably shorter and broader, and in Mrassiella kemeroviensis—long and narrow.

Occurrence: the Dvoinoi-Intermediate seam.

Mrassiella umbonata sp. n.

Plate 1, fig. 12.

Holotype: TPI Collection, museum number 282. Kuznetsk Basin, Kemerovo district, Intermediate Subformation.

Description. Shell of medium size, oval-obliquely shield-shaped, moderately convex; the greatest convexity is in the near-umbonal and central part, whence the surface slopes gently toward the anterior-ventral and posterior margins of the shell. The hinge margin is straight, about 2/3 of the greatest length of the shell, and joins the anterior and posterior margins through rounded angles. The angle between the hinge and posterior margins is about 120°. The umbo is very high, massive, somewhat shifted toward the anterior margin.

The angle between the direction of the main diagonal and the hinge margin is 65°.

The anterior-ventral and posterior margins are outlined by smoothly convex arcs. The lower posterior angle is incompletely preserved; judging from the course of the growth marks, it is somewhat compressed. The greatest height passes through the upper posterior angle and is almost equal to the length of the shell. The surface of the shell is covered with concentric ridges, very regular and gently sloping, clearer near the margins of the shell; very fine concentric lines pass over them.

Dimensions: length — 14.5 mm; height — 14 mm.

Comparisons. We have at our disposal a rather completely preserved internal mold of a left valve and its external impression. The form described, in outline and sculpture, is very similar to Mrassiella magniforma Rag. forma permagna Khalf.; however, it is very clearly distinguished from this species and from other species of the genus Mrassiella by its large, massive umbo, raised high above the hinge margin.

Occurrence: between the Kutashovo and Lyzhinsky seams.

Mrassiella sp. n., cf. M. concinna Khalfin.

Plate 1, fig. 13.

Description. Shell of medium size, oval, somewhat oblique, weakly convex.

The hinge margin is straight in front of the umbo and somewhat inclined behind it; it amounts to \(3/4\) of the greatest length of the shell. The umbo occupies a subcentral position on the hinge margin and is slightly inclined forward. The upper angles are cut off by broad roundings.

The anterior margin of the shell is outlined by a regular convex arc. The posterior margin forms with the hinge margin an indistinctly expressed angle of \(150^\circ\), and is outlined by a somewhat more convex arc than the anterior one. The lower posterior angle has not been preserved, but, judging from the growth marks, it has rounded outlines.

The angle between the hinge margin and the direction of the main diagonal is \(50^\circ\). The greatest height of the shell passes through the upper posterior angle and is close to its length.

The sculpture is represented by dense, fine, numerous concentric lines and by a few flat, broad concentric ribs.

Dimensions: length—20 mm; height—17 mm.

Comparisons. From typical representatives of Mrassiella concinna Khalfin [6, p. 57] it differs in its larger size, more rounded outlines, and more rounded auricles.

From Mrassiella magniforma it differs in its broader shell, lesser development along the main diagonal, more rounded and broad lower-posterior angle, and also in the different character of the sculpture.

Locality: 4 m above the Dvoynoy-Promezhutochnyi bed.

CITED LITERATURE

1. Benediktova R. N. The first find of the Alykayev pelecypod fauna beyond the limits of Kuzbass. Trudy Tomskogo universiteta im. V. V. Kuibysheva, vol. 132, 1954.

2. Neuburg M. F. Upper Paleozoic flora of the Kuznetsk Basin. Paleontologiya SSSR, vol. XII, part 3, issue 2, 1948.

3. Ragozin L. A. Pelecypods of the Balakhon Formation of Kuzbass. Trudy Tomskogo universiteta im. V. V. Kuibysheva, vol. 88, 1935.

4. Fedotov D. M. Lamellibranch mollusks of the coal-bearing deposits of the Kuznetsk Basin. Trudy Tsentralnogo nauchno-issledovatelskogo geologorazvedochnogo instituta, issue 97, 1937.

5. Fedotov D. M. Pelecypods from coal-bearing deposits, chiefly of the industrial regions of the Kuznetsk Basin. Izvestiya AN SSSR, Biology Series, No. 1, 1938.

6. Khalfin L. L. Lamellibranch mollusks of the coal-bearing deposits of Kuzbass. Trudy Gorno-geologicheskogo instituta Zap.-Sib. filiala AN SSSR, issue 9, 1950.

7. Khalfin L. L. Lamellibranch mollusks of the Baidayevka deposit (Kuzbass). Izvestiya Tomskogo politekhnicheskogo instituta im. S. M. Kirova, vol. 65, issue 2, 1950.

Tomsk Polytechnic Institute
named after S. M. Kirov

Explanation of the Plate of Photographic Illustrations

All the forms illustrated come from the Intermediate Subformation of the West-Butovo sector of the Kemerovo District.

Fig. 1. Anthraconauta tenuistriata sp. n. Impression of the external surface of the left valve (specimen 169-6).

Fig. 2. Anthraconauta tenuistriata sp. n. Impression of the external surface of the left valve (specimen 168).

Fig. 3. Anthraconauta klepovi sp. n. Internal mold of the right valve (specimen 191).

Fig. 4. Anthraconaja sp. Internal mold of the right valve (specimen 185).

Fig. 5a, 5b. Anthraconauta (?) mrassiellaeformis sp. n. 5a—internal mold of the right valve, 5b—impression of the external surface (specimen 169-8).

Fig. 6a, 6b — Anthraconauta pseudolongissima sp. n. 6a—internal mold of the right valve, 6b—impression of the external surface (specimen 157).

Fig. 7. Anthraconauta cf. sibirica (Rag.). Internal mold of the left valve (specimen 169).

Fig. 8. Anthraconauta butovi sp. n. Impression of the external surface of the right valve (specimen 281).

Fig. 9. Anthraconauta obliquilingualis sp. n. Internal mold of the left valve (specimen 321).

Fig. 10. Kinerkaella oblonga (Rag.). Internal mold of the left valve (specimen 307).

Fig. 11a, 11b, 11c—Kinerkaella cf. balakhonskiensis Khalf. 11a—internal mold of the right valve, 11b—impression of the external surface, 11c—the same, enlarged (specimen 164).

Fig. 12. Mrassiella umbonata sp. n. Internal mold of the right valve (specimen 282).

Fig. 13. Mrassiella sp. n., cf. M. concinna Khalf. Impression of the external surface of the left valve (specimen 304).

Fig. 14a, 14b Mrassiella kemeroviensis sp. n. 14a—impression of the external surface of the right valve, 14b—internal mold of the right valve (specimen 170).

Fig. 15a, 15b. Mrassiella kemeroviensis sp. n. 15a—internal mold of the right valve, 15b—impression of the external surface (specimen 259).

Table 1

1

2

3

4

5a

5b

6a

6b

7

8

9

10 × 2

11a × 2.5

11b × 2.5

12

13

14a

14b

15a

15b

11v × 10

1. The section of the deposits of the Butovka-Western area is given in Fig. 2 in N. M. Belyanin’s paper published in the present volume. (Editor’s note). ↩