Pelecypods from the Jurassic and Cretaceous Deposits of the Kuznetsk and Chulym–Yenisei Basins

I. V. Lebedev

Introduction

The continental Mesozoic deposits of Western Siberia contain numerous remains of plants, lamellibranch mollusks, gastropods, crustaceans, fishes, insects, dinosaur remains, and others. This organic world of the Mesozoic has been studied very unevenly. Whereas an extensive literature is devoted to the study of the Mesozoic flora, the fauna has been almost unstudied. All the literature on the Mesozoic fauna of Western Siberia is limited to descriptions of several species of lamellibranch mollusks, phyllopods, and insects from the Kuznetsk and Chulym–Yenisei basins. Yet even this very scanty literature shows that the fauna of the continental Mesozoic deposits is an important means for correlating sections even of distant regions. Thus, on the basis of the insect and fish fauna the Jurassic of the Irkutsk and Kuznetsk basins is well correlated; on the basis of the pelecypod fauna, the Triassic of the Kuznetsk and Tunguska basins, the Lower Cretaceous of Western Siberia and Western Europe, and so forth.

Among the Mesozoic fauna of Western Siberia, the most widespread are pelecypods, which are very often encountered in cores obtained during drilling in coal deposits; consequently, they have been studied better. At present, 7 works are devoted to this fauna. However, the Mesozoic pelecypod fauna is not always well preserved, and therefore new collections often lead to additions to and revisions of previous descriptions.

The author of the present article, thanks to the assistance of the Krasnoyarsk party of the trust “Vostsibuglegeologiya,” of the Siberian branches of the Academy of Sciences and of VNIGRI, over a number of years had the opportunity to collect and study the Mesozoic pelecypod fauna; as a result, considerable material was accumulated, making it possible to supplement and correct some previously completed works. This article gives a characterization of the generic composition of this fauna, illustrated by photographs of the most widespread and most typical species.

The continental Mesozoic of Western Siberia has a complex composition. It includes Triassic, Jurassic, and Cretaceous deposits. The Triassic deposits, known under the name of the Maltsevo Formation, occur in the central region of the Kuzbass. They consist of sedimentary and tuffaceous rocks of Lower Triassic and, in part, possibly Middle Triassic age.

The Jurassic of Western Siberia is composed of a coal-bearing sequence; all three divisions are present in it. The Cretaceous deposits, very widely distributed in the Chulym–Yenisei depression, consist of sequences closely connected with the redeposition of products of chemical weathering.

The age of all Mesozoic suites has been established from fossil flora and insect fauna.

A comparison of the stratigraphic schemes of the Mesozoic of the Kuznetsk and Chulym–Yenisei basins is given in the following table.

Table

Composition and distribution of the pelecypod fauna of the continental Mesozoic of Western Siberia

Only six works by L. A. Ragozin and one work by G. G. Martinson are devoted to the pelecypod fauna of the continental Mesozoic of Western Siberia. In 1931, L. A. Ragozin [5] described from the Jurassic of Kuzbass a single shell under the name Posidonomya sp. Later L. A. Ragozin [6] described, from the Jurassic deposits of Kuzbass, 13 new species belonging to the new genus Tutuella Ragozin; moreover, he included in this genus the form described earlier under the name Tutuella tomiensis.

In 1954 L. A. Ragozin published a new work in which, as the author states, he revised his earlier determinations. In this work L. A. Ragozin [8] gives a description of 23 species assigned to the genera Unio, Tutuella, and Ferganoconcha. In another work, published in the same year, L. A. Ragozin [9] mentions the discovery, in the Maltsevskaya suite of Kuzbass, of shells of Utschamiella Ragozin, previously described from the Tunguska basin, and in the guide to the fossil fauna of Western

Siberia, they [10] indicate that the Jurassic of the Kuzbass contains certain species of the genera Unio, Ferganoconcha, Tutuella, described in other works, and in the Triassic—Utschamiella tungussica Ragozin. Finally, in his most recent work L. A. Ragozin [11] indicates that the Triassic of the Kuzbass contains two additional new species of Utschamiella and two new species of Ferganoconcha. Thus, according to L. A. Ragozin, the general list of the pelecypod fauna of the Mesozoic of the Kuzbass includes 28 species belonging to the genera Unio Phillipson, Tutuella Ragozin, Ferganoconcha Chernyshev, and Utschamiella Ragozin, which he includes in the family Unionidae. In G. G. Martinson’s work, descriptions are given of four species of pelecypods belonging to the genus Ferganoconcha from the Chulym-Yenisei basin, one of which is new.

At the present time, the pelecypod fauna of the continental Mesozoic includes representatives of the genera: Unio Phillipson, Anunio gen. nov., Cyrena Lamarck, Acyrena gen. nov., Pisidium Pfeiffer, Naiadites Dawson, Tutuella Ragozin, Ferganoconcha Chernyshev, Sibireconcha gen. nov., and Kija gen. nov., belonging to the families Unionidae, Cyrenidae, Myalinidae, and to pelecypods of uncertain systematic position.

Family Unionidae Fleming.
Genus Unio Phillipson, 1788.
Pl. I; Pl. II, figs. 4—6.

The shell of this genus is equivalved, inequilateral, highly variable in shape, more often elongated in length. The surface of the valves is smooth, more rarely ornamented with ribs, folds, and tubercles. The hinge is highly variable. On the right valve there is most often one radially striated cardinal tooth and a long posterior lamellar tooth. The hinge of the left valve consists of two cardinal and two posterior lamellar teeth, covered with striae and grooves. The anterior adductor muscle forms a deep depression on the valves; the impression of the posterior adductor muscle is less deeply impressed. The pallial line is simple.

The genus Unio appears in the Triassic deposits of America, Western Europe, and Australia. In the territory of the USSR, reliably established Unio were previously known from the Jurassic of the Irkutsk and Chelyabinsk basins, from the Lower Jurassic coal-bearing deposits of Fergana [13], and from the Jurassic of the Kuzbass [6; 10; 11]. Apparently, the Lower Triassic genus Utschamiella Ragozin [7; 10] also belongs to this same genus. In L. A. Ragozin’s opinion, the shells of this genus differ from shells of Unio in their smaller size, low, distinctly forward-inclined umbones, and lesser convexity of the valves. Exactly the same shells occur in Unio dockumensis Simpson, Unio dumbei Simpson, and others from the Triassic of North America, but the hinge apparatus of Utschamiella is not yet known, in connection with which its inclusion in the genus Unio is premature. If representatives of the genus Utschamiella are excluded, then the genus Unio in Western Siberia is known to us only from the Middle Jurassic; within this genus 20 species are known, the majority of them new (see the distribution table, p. 217).

Anunio gen. nov.
Pl. II, figs. 1—3.

The shells are large, convex, thick-valved, oval. The umbones are subcentral, massive, high, slightly inclined forward. The hinge margin is curved. The shell margins are convex. The hinge is heterodont. On each valve there is one cardinal tooth and two posterior lateral teeth. The ligament is external, long. The surface of the valves is covered with concentric growth marks, radial ribs, and folds.

In the character of the hinge, Anunio is closest to the genus Unio Phill., although it differs from this genus in a number of essential features. Thus, whereas in Unio there is one posterior lateral tooth on the right valve, in Anunio there are two; in Anunio the cardinal teeth are strongly displaced toward the anterior margin, whereas in Unio they are situated beneath the umbo or near it, etc.; but the general plan of the hinge structure is very close to that of Unio, and therefore the assignment of Anunio to the family Unionidae is beyond doubt.

In the general outline of the shells and in the character of the sculpture, Anunio is close to the shells described by G. G. Martinson as Protounio Martinson [3], which likewise have a convex oval shell, protruding umbones, and radial ribs; but cardinal teeth are absent in that genus, and on both sides of the umbo there are paired lateral teeth covered with fine notching.

This genus is so far represented by only one species, Anunio ananjevi gen. et sp. n., found in the Kiya Formation.

The shells of this genus have a transversely oval or triangular form, often with a well-expressed keel and concentric sculpture. The umbones are high, the hinge margin is not straight. The hinge is heterodont, highly variable. In general, each valve has three cardinal teeth. The lateral teeth are lamellar; on the right valve they are double, on the left valve single. They appear in the Triassic and persist to the present day. In Western Siberia, cyrenids appear in the Lower Jurassic deposits. At present, six species of cyrenids are known to us from the Mesozoic of Western Siberia: Cyrena kemtschugensis sp. n., Cyrena korkinensis sp. n., Cyrena subtransversa Röm., Cyrena (?) sibirensis sp. n., Cyrena (?) elongata sp. n., Cyrena karaldinensis sp. n.

The shells of this genus are thin-walled, have an elongate-oval form, and are covered with fine growth marks. In modern representatives of this genus the anterior margin is shorter than the posterior. In ancient forms the posterior margin is longer. The hinge is heterodont. On the left valve, beneath the umbo, there are two cardinal teeth, and in front of and behind the umbo there is one lamellar tooth each. On the right valve there are likewise two cardinal teeth, but there are two lateral teeth in front of and behind the umbo. In Western Siberia this genus appears already in the Middle Jurassic. At present the following species are known within the genus: Pisidium tjazhinense sp. n., Pisidium (?) kochantchikii sp. n., Pisidium (?) elegans sp. n.

The shells are thick-valved, inequilateral, elongated, subtriangular, quadrangular, oval, or rhomboidal, equivalve, and covered with concentric growth marks. The umbones are shifted toward the anterior end of the hinge margin, convex. The hinge margin is not straight, long. The hinge is heterodont. On the right valve, behind the umbones, there are two thin, long lateral teeth; in front of the umbo there is one short lateral tooth. On the left valve, in front of and behind the umbo, there is one lateral tooth each. There are cardinal teeth on each valve in ...

one. The pallial line at the lower posterior angle forms a shallow sinus. The surface of the shells is covered with growth marks.

Genotype. Acyrena jenissejensis gen. et sp. n.

In the structure of the hinge, shells of Acyrena resemble Unio and Cyrena, but Unio lacks anterior lamellar teeth, the paired lateral teeth are situated on the left valve, and the cardinal tooth of the left valve is split into two teeth. The genus Cyrena differs in that each valve has three cardinal teeth, although sometimes these teeth merge into a single tooth; however, the fused teeth have notches, and the cyrenid type of hinge is preserved in them. At present the genus includes 5 species: Acyrena jenissejensis sp. n., Acyrena rhomboidea sp. n., Acyrena tetragonalis sp. n., Acyrena busimensis sp. n., Acyrena murtinensis sp. n.

Family Myalinidae Frech, emend. Newell

Genus Naiadites Dawson, 1860.
Plate III, fig. 23.

The shell of this genus is inequivalve and inequilateral. The left valve is more convex than the right. The anterior margin is beveled backward. The hinge margin is straight and long; the hinge area bears longitudinal grooves. In the anterior part of the hinge area there is one cardinal tooth. The tooth of the left valve is situated closer to the umbo. The umbones are located near the anterior margin. From the umbo to the posterior angle runs a sharply expressed keel. On the anterior margin of the valves there is a sinus for the exit of the byssus. The pallial line consists of a series of small depressions. The scar of the anterior adductor, in the form of a small pit, is situated near the umbo. The scars of two accessory umbonal impressions are situated between the anterior adductor and the umbo. The posterior adductor lies near the posterior margin. The surface is covered with growth marks.

Representatives of the genus Naiadites on the territory of the USSR appeared in the coal-bearing deposits of the Donets Basin and are widely distributed in the Carboniferous and Permian of the Kuzbass. L. A. Ragozin [11] considers that the genus Naiadites is characteristic only of the Carboniferous, but individual naiaditids in Siberia have also been found in the Il’inskaya Suite. In North America Naiadites occurs in the Upper Triassic. They were not known from younger deposits. In the Mesozoic of Western Siberia there is one species, Naiadites krasnojarskiensis sp. n.

Pelecypods of uncertain systematic position

Tutuella Ragozin, 1937.
Plate III, figs. 8—9.

The shells are convex, oval, more rarely elliptical in shape, and are covered with fine growth marks. The umbones are massive, subcentral, and project only slightly above the hinge margin. The hinge margin is curved, sometimes nearly straight. The ligament is external, long, and extends on both sides of the umbones (amphidetic). The structure of the hinge is unknown.

The diagnosis of the genus Tutuella given above differs somewhat from the diagnosis given for it by L. A. Ragozin. L. A. Ragozin believed that the hinge margin in tutuellas is straight, but study of the most complete specimens shows that the latter have a nonstraight hinge margin. In addition, the very scope of the genus Tutuella was not precisely defined by L. A. Ragozin. L. A. Ragozin included in this genus shells having different forms, and thereby gave the genus a broad interpretation.

The characterization given above considerably narrows the scope of this genus. In this case, such species as the following should be excluded from it:

Tutuella elegans Rag., Tutuella gigantea Rag., Tutuella paradoxa Rag., Tutuella fabialis Rag., Tutuella ovalis Rag., Tutuella tomiensis Rag., and Tutuella balbinskiensis Rag. [6]. Within the genus Tutuella may be retained Tutuella crassa Rag., Tutuella iraidae Rag., Tutuella rotunda Rag., and, perhaps, Tutuella chachlovi Rag., as well as the new species Tutuella sibirensis sp. n. and Tutuella trapezoidalis sp. n.

The shells of tutuellae are known only as external molds; their internal structure has not been studied, and therefore their systematic position is unknown. L. A. Ragozin [6] suggested that this genus belongs to the unionids, which, however, is unlikely, since such a shell form is not characteristic of the family Unionidae. In the outline of the shell the tutuellae stand closest to the cyrenids, specifically to the genera Corbicula Megerle and Sphaerium Scopoli, but apparently, unlike them, the hinge margin in Tutuella Ragozin lacks teeth.

G. G. Martinson [4] unites the genus Tutuella, together with Ferganoconcha, in the family Ferganoconchidae; however, the shell forms of these two genera are sharply different, their hinges are unknown, and therefore such a union cannot be considered successful.

Genus Ferganoconcha Chernyshev, 1937

Shells of this genus are elliptical and obliquely elliptical in outline, weakly convex. The hinge margin is straight and long. The beaks are situated closer to the anterior margin or are almost central; they do not project above the hinge margin. The keel is absent. The ligament is external, amphidetic. The surface of the valves is wrinkled. Growth marks are fine and dense. The internal structure is unknown.

The systematic position of the genus Ferganoconcha has not been clarified. It is possible that the genus is a composite one, artificially uniting all small, crushed, and flat shells of elliptical form.

Representatives of the ferganoconchs appear in Lower Jurassic deposits of northern Asia and are widely distributed in all coal-bearing basins of Jurassic and Lower Cretaceous age. In younger and older deposits ferganoconchs are unknown. Outside the Soviet Union ferganoconchs have not been described. The Jurassic deposits of western Siberia contain: Ferganoconcha jorkensis Chern., Ferganoconcha sibirica Chern., Ferganoconcha subcentralis Chern., Ferganoconcha jeniseica Martinson, Ferganoconcha minor Martinson. It is characteristic that in western Siberia this entire fauna occurs only in the Middle Jurassic.

Genus Sibireconcha n. gen.

Plate III, figs. 1—7.

Shells small, weakly convex, elongated. The beaks are massive, situated closer to the anterior margin, and project only slightly above the hinge margin. The hinge margin is slightly curved, long. The anterior margin is short; with the lower and posterior margins it forms smooth curves. The lower margin is long, sometimes straight in its middle part. The lower posterior angle is drawn back and pointed. The posterior margin is weakly convex; with the hinge margin it forms an obtuse angle, and with the lower margin an acute angle. The ligament is external, thin, opisthodetic. The surface is covered with fine growth marks. The hinge is heterodont (?). Behind the beaks on the right valve there is one lateral tooth, and on the left valve there are two lateral teeth. The cardinal teeth are unknown.

Among the numerous pelecypod remains in the Jurassic deposits, impressions or sculptural molds of small shells are not infrequently encountered, elongated and having their characteristic lower posterior angle drawn back and pointed. These include: Ferganoconcha ano-

dontoides, and others. Such shells were included by B. I. Chernyshev and L. A. Ragozin in the genus Ferganoconca Chern. However, as B. I. Chernyshev himself indicated [13, 14], the characteristic diagnostic feature of shells of the genus Ferganoconcha is an elliptical or co-elliptical form. Shells strongly developed in length, which do not fit this definition and were artificially included in the genus Ferganoconcha, are here proposed to be separated into a new genus, Sibireconcha, which, as indicated above, has features of a heterodont hinge.

In external outline the shells of some species of Sibireconcha are very similar to shells described by Grabau from the Lower Cretaceous of China (the Mengyin series) as various species of the genus Mycetopus Orb. It is possible that such species as Mycetopus mengyinensis Grabau [18] and Sibireconcha lankoviensis sp. n. are even genetically closely related, but comparison of them is as yet premature.

In external form the shells of Sibireconcha have some similarity with the Upper Paleozoic genera Antraconaia Truem. et Weir and Anthraconauta Pruvost [12].

Genotype. Sibireconcha lankoviensis gen. et sp. n.

Within this genus, 15 species are known in the Mesozoic of Western Siberia.

Kija gen. nov.

Table III, figs. 18—21.

Shells small, convex, oval or rounded-triangular, thin-walled. Umbones protruding, sharp, curved forward. Escutcheon and lunule not expressed. Hinge margin long, curved. Hinge highly variable. Cardinal teeth absent. On the right valve, in front of and behind the umbo there is usually one lamellar tooth each; on the left valve, usually in front of and behind the umbo there appear two weak lamellar teeth each. Muscle scars deep. The anterior adductor muscle is situated in front of the umbo and has an oval form. The posterior adductor muscle has a spindle-shaped form, elongated obliquely downward, parallel to the posterior lamellar tooth. Mantle line simple. The surface of the valves is covered with thin but sharp growth marks and rare, gentle ribs formed by uneven accretion.

The shell form of this genus is rather variable and in general falls into two types. Most commonly encountered are strongly inflated, rounded-triangular shells. The umbones of such shells are sharp, protruding, curved forward, and inclined toward the hinge margin. From the umbones to the posterior lower angle there usually runs a clearly expressed keel. In the other type the shells have an oval form, less convex valves, and weakly protruding umbones. The keel in these shells is almost imperceptible.

In the structure of the hinge in Kija two types can also be observed—complete and incomplete hinges. The complete hinge, which occurs more rarely, on the right valve, in front of and behind the umbones, has one well-expressed protruding lamellar tooth each; below and above it there are narrow and very shallow grooves corresponding to the lamellar teeth of the left valve. It is characteristic that the anterior tooth of the right valve is always slightly curved, passes through the umbonal part of the hinge plate, bends downward, and merges with the lower edge of the hinge plate.

The more frequently occurring type of hinge on the right valve, in front of and behind the umbo, has one lamellar tooth each, and on the left valve, correspondingly in front of and behind the umbo, one dental pit each.

Comparing these two types of hinge, one may say that in general in this genus the right valve has one anterior and one posterior lamellar tooth, while on the left valve, in front of and behind the umbo, correspondingly—

...the corresponding dental pits, but sometimes the edges of the hinge plate of the left valve become sharpened and turn into additional lamellar teeth, while on the right valve, on the sides of the lamellar teeth, small depressions appear—the dental pits corresponding to the marginal lamellar teeth.

The systematic position of the genus Kija is unknown. Of all fossil shells, some cyrenids and unionids are close to this genus. It is brought close to the former by the rounded-triangular form of the shells and the sharp umbones. But all cyrenids differ in the structure of the hinge apparatus, namely in the presence of cardinal teeth, whereas in Kija there are no signs whatever of such teeth. Moreover, the above-mentioned passage of the anterior tooth of the right valve across the hinge plate generally excludes the possibility of the appearance of cardinal teeth similar to the teeth of cyrenids.

The genus Kija, on the contrary, is brought close to the unionids by the structure of the hinge. Representatives of the family Unionidae, as is known, have a very diversely constructed hinge. In some genera, as for example Protounio, the modification of the teeth reaches such a degree that on the hinge plate of the right valve there remain only the anterior and posterior lateral teeth, not interrupted beneath the umbo, while on the left valve bifid lamellar teeth appear. It might be supposed that the anterior tooth of the right valve of Kija, passing through the umbonal part, corresponds to the lateral teeth of the right valve of unionids, and that the posterior tooth of the right valve of Kija corresponds to the posterior tooth of Unio. The teeth of the left valves of fully toothed forms, as indicated above, can likewise be compared with the double teeth of the left valves of some unionids. This resemblance is further increased by the fact that striation appears on the teeth of Kija (additional denticulation), so characteristic of unionids. The exceptionally great peculiarity of Kija will apparently lead to the establishment of a special family, but additional studies are required for this.

Genotype. Kija tjazhinensis gen. et sp. n.

Within the genus Kija, the following species are presently known: Kija tjazhinensis sp. n., Kija kibetenensis sp. n., Kija miroschnichenkii sp. n., Kija elongata sp. n., Kija elliptica sp. n.

CITED LITERATURE

1. Bogachev V. V. Freshwater fauna of Eurasia. Part I. Transactions of the Geological Committee, new series, issue 135. 1924.

2. Lebedev I. V. On some lamellibranchs from the Kolchugino Suite of Kuzbass. Izvestiya of the Academy of Sciences of the USSR, biological series, No. 2. 1944.

3. Martinson G. G. New unionids from the Upper Cretaceous deposits of Mongolia. Reports of the Academy of Sciences of the USSR, vol. 89, No. 1. 1953.

4. Martinson G. G. Key to Mesozoic and Cenozoic freshwater mollusks. Academy of Sciences of the USSR. 1956.

5. Ragozin L. A. Lamellibranchs from coal-bearing deposits of the southern part of the Kuznetsk Basin. Transactions of the Scientific-Research Coal Institute of Vostokugol, series G, issue 1. 1931.

6. Ragozin L. A. First finds of lamellibranchs from the Jurassic deposits of Kuzbass. Transactions of Tomsk State University named after V. V. Kuibyshev, vol. 93. 1937.

7. Ragozin L. A. On some pelecypods from the coal-bearing series of the Tunguska Basin. Transactions of Tomsk State University named after V. V. Kuibyshev, vol. 93. 1937.

8. Ragozin L. A. Lamellibranch mollusks from Jurassic coal-bearing deposits of Kuzbass. Transactions of Tomsk State University, vol. 132. 1954.

9. Ragozin L. A. New data on bivalve mollusks from the coal-bearing deposits of Kuzbass. Transactions of Tomsk State University, vol. 132. 1954.

10. Ragozin L. A. Pelecypods of the Triassic and Jurassic of Kuzbass. Atlas of guide forms of fossil fauna and flora of Western Siberia, vol. II. Gosgeoltekhizdat. Moscow. 1955.

1. Ragozin L. A. Triassic and Jurassic pelecypods from the coal-bearing deposits of the Angara continent. Proceedings of Tomsk State University, vol. 135. 1956.

2. Khalfin L. L. Lamellibranch mollusks of the coal-bearing deposits of Kuzbass. West Siberian Branch of the Academy of Sciences of the USSR. Proceedings of the Mining-Geological Institute, issue 9, 1950.

3. Chernyshev B. I. On some Jurassic lamellibranchs from Fergana. Proceedings of the Central Asian Geological Trust, issue 1. 1937.

4. Chernyshev B. I. On some pelecypods from Transbaikalia and the Far Eastern Territory. Proceedings of the All-Union Scientific Research Institute of Mineral Raw Materials, issue 143. 1939.

5. Branson C. C. Fresh-Water invertebrates from Merrison (Jurassic?) of Wyoming. Journ. of Paleontology, vol. 9, No. 6. 1935.

6. Dunker W. Monographie der Norddeutschen Wealdenbildung. 1846.

7. Forbes E. On the Estuary Beds of the Oxford Clay at Loch Staffin, in Skye. The Quarterly Journal of the Geological Society of London, vol. 7. 1851.

8. Grabau A. W. Cretaceous Fossils from Shantung. Bull. of the Geological Survey of China, No. 5, part 2. 1923.

9. Grabau A. W. Contribution to the Fauna of the Kweichou formation of central China. Bull. of the Geological Survey of China, No. 5, part 2, 1923.

10. Henderson I. Fossil non-marine Mollusca of North America. Geol. Soc. of America. Special Papers, No. 3. 1935.

11. Kobayashi T. and Suzuki K. Non-marine shells of the Nactong Wakino Series. Japanes journal of Geology and Geography, vol. 13, No. 3—4. 1936.

12. Kobayashi T. and Suzuki K. Non-Marine Shells of the Nactong Jurassic Tetori Series in Japan. Jap. Journ. of Geology and Geography, vol. 14, No. 1—2. 1937.

13. Römer F. A. Die Versteinerungen des Norddeutschen Oolithen Gebirges. 1836.

14. Römer F. A. Die Versteinerungen des Norddeutschen Oolithen Gebirges. Ein Nachtrag. 1839.

15. Sandberger F. Die Land und Süsswasser-Cochylien der Vorwelt. 1870—1875.

16. Simpson Ch. T. Description of four new Triassic Unios from the Staked plains of Texas. Un. St. Nat. Museum Proceedings, vol. 18. 1895.

17. Sowerby. Mineral Conchology of Great Britain. Vol. VI. 1844.

18. White C. A. On the fresh-water invertebrates of the North America, Jurassic. U. S. geol. Survey. Bull. 29. 1886.

19. White C. A. A review of the Non-marine fossil Mollusca of North America. U. S. Geol. Surv., 3-rd Annual Report. 1883.

20. Zittel K. Die Bivalven der Gosaugebilde in den Nordostlichen Alpen. Abh. der k.-k. Acad. d. Wissensch. Math.-naturwiss. Cl. XXIV, 1864.

Tomsk Polytechnic Institute
named after S. M. Kirov

Vertical distribution of pelecypods

EXPLANATION OF THE PLATES

Plate I

1. Unio golovae sp. n. Right bank of the Bolshaya Chernaya River, 2 km east of Chernorechenskaya station. Ilek Formation. Holotype. Internal mold. Natural size.

2. Unio tschulymensis sp. n. Right bank of the Bolshaya Chernaya River, 2 km east of Chernorechenskaya station. Holotype. Internal mold. Natural size.

3. Unio ragosini sp. n. Right bank of the Bolshaya Chernaya River, 2 km east of Chernorechenskaya station. Internal mold. Natural size.

4. Unio jenissejensis sp. n. Left bank of the Yenisei River, 2 km upstream from the village of Barabanovo. Upper subformation of the Itat Formation. External mold. × 1.1.

5. Unio sartakoviensis sp. n. Kuzbass, Stepnoi Urop River, 1 km upstream from the village of Sartakovo. Sartakovo unit of the conglomerate formation. Holotype. External mold. × 1.3.

6. Unio tyjensis sp. n. Right bank of the Kemi River, 4 km upstream from the settlement of Kholovskogo. Suchkovo subformation. Impression of the right valve. Holotype. × 1.2.

7. Unio kemensis sp. n. Right bank of the Kemi River, 5 km upstream from the mouth. Suchkovo subformation. Impression of the right valve. Holotype. Natural size.

8. Unio kubekoviensis sp. n. Left side of Lankov Log in the village of Kubekovo on the left bank of the Yenisei. Upper subformation of the Itat Formation. Impression of the left valve. Natural size.

9. Unio barabanowskiensis sp. n. Left bank of the Yenisei River, 2 km upstream from the village of Barabanovo. Upper coal-bearing subformation of the Itat Formation. External mold. Natural size.

10. Unio tomiensis sp. n. Left bank of the Yenisei River, 3.3 km downstream from the village of Chernyi Etap. Sartakovo unit of the conglomerate formation. Holotype. × 1.1.

11. Unio jatchevskii sp. n. Left bank of the Yenisei River in the village of Kubekovo. Upper subformation of the Itat Formation. Impression of the left valve. × 1.1.

Plate II

1–3. Anunio ananjevi gen. et sp. n. Kiya River at the mouth of the Serta River. Kiya Formation. External mold from the type cast. Natural size. Fig. 3—impression of the sculpture of the lower margin of the valve.

1. Unio kaziaevi sp. n. Right bank of the Uryup River, 4 km downstream from the village of Staryi Uryup. Ilek Formation. Left valve. Holotype. × 2.

2. Unio urjupiensis sp. n. Right bank of the Uryup River, 4 km downstream from the village of Staryi Uryup. Ilek Formation. Holotype. × 1.4.

3. Unio khomentovskii sp. n. Left bank of the Yenisei River below the city of Krasnoyarsk, opposite the lower end of Tatyshev Island. Makarovo Formation. External mold. × 2.3.

4. Acysena jenissejensis sp. n. Left bank of the Yenisei River in the village of Khudonogovo. Upper subformation of the Itat Formation. Holotype. × 2.

1. Acyrena busimensis sp. n. Village of Khudonogovo on the left bank of the Yenisei River. Upper subformation of the Itat Formation. Holotype. Natural size.

2. Acyrena murtnensis sp. n. Village of Tatarskaya, Sukhobuzim District, borehole 42 near 147–150. Upper subformation of the Itat Formation. Holotype. ×1.5.

3. Acyrena tetragonalis sp. n. Village of Khudonogovo on the left bank of the Yenisei River. Upper subformation of the Itat Formation. Holotype. Natural size.

4. Acyrena rhomboidea sp. n. Village of Khudonogovo on the left bank of the Yenisei River. Upper subformation of the Itat Formation. Holotype. ×1.2.

Plate III

Fig. 1. Sibireconcha lankoviensis sp. n. Left bank of Lankov Log in the village of Kubekovo on the left bank of the Yenisei. Upper subformation of the Itat Formation. External mold. ×1.2.

Fig. 2. Sibireconcha sitnikovae sp. n. Right bank of the Bolshoi Kemchug River in the village of B. Kemchug. Makarovo Formation. External mold. Holotype. ×2.

Fig. 3. Sibireconcha kemtschugensis sp. n. Right bank of the Bolshoi Kemchug River in the village of B. Kemchug. Makarovo Formation. External mold. Holotype. ×2.5.

Fig. 4. Sibireconcha jenissejensis sp. n. Lankov Log in the village of Kubekovo. Upper subformation of the Itat Formation. External mold. ×1.3.

Fig. 5. Sibireconcha bogdanovitchi sp. n. Lankov Log in the village of Kubekovo. Upper subformation of the Itat Formation. ×1.4.

Fig. 6. Sibireconcha brevis sp. n. Right bank of the Bolshoi Kemchug River in the village of Bolshoi Kemchug. Makarovo Formation. Holotype. ×3.

Fig. 7. Sibireconcha kusbassica sp. n. Kuzbass, right bank of the Bolshaya Karalda River, 6 km downstream from the village of Karalda. Karalda unit. External mold. Holotype. ×2.

Fig. 8. Tutuella sibirensis sp. n. Left bank of the Yenisei River, 0.5 km upstream from the village of Khudonogovo. Upper subformation of the Itat Formation. External mold. Holotype. ×2.

Fig. 9. Tutuella trapetzoidalis sp. n. Left bank of the Yenisei River, 2 km upstream from the village of Barabanovo. External mold. Holotype. ×2.2.

Fig. 10. Pisidium tjazhinense sp. n. Tyazhin, borehole 1, depth 96–102. Tyazhin Formation. External mold. Holotype. ×2.5.

Fig. 11. Pisidium kochantchikii sp. n. Krasnoyarsk District, borehole 33, depth 194–196. Upper subformation of the Itat Formation. External mold. Holotype. ×2.5.

Fig. 12. Pisidium elegans sp. n. St. Tyazhin, borehole 4, depth 102. Ilek Formation. External mold. Holotype. ×2.5.

Fig. 13. Cyrena sibirensis sp. n. Left bank of the Yenisei River, 0.5 km downstream from the village of Kubekovo. Upper subformation of the Itat Formation. External mold. Holotype. Natural size.

Fig. 14. Cyrena karaldinensis sp. n. Kuzbass, right bank of the Bolshaya Karalda River, 6 km downstream from the village of Karalda. Karalda unit. External mold. Holotype. ×1.4.

Fig. 15. Cyrena elongata sp. n. Left bank of the Yenisei River, 0.5 km upstream from the village of Khudonogovo. Upper subformation of the Itat Formation. External mold. Holotype. ×2.

Fig. 16. Cyrena korkinensis sp. n. Krasnoyarsk District, borehole 33, depth 169.4–196. Upper subformation of the Itat Formation. External mold. ×2.

Fig. 17. Cyrena kemtschugensis sp. n. Right bank of the B. Kemchug River, 3.5 km downstream from the village of B. Kemchug. Upper subformation of the Itat Formation. External mold. Monotype. ×2.8.

Fig. 18. Kija elliptica sp. n. Kibeten mulda, borehole 831, depth 163. Tyazhin Formation. Holotype. ×2.

Fig. 19. Kija elongata sp. n. Kibeten mulda, borehole 834, depth 136. Tyazhin Formation. Holotype. ×2.

Fig. 20. Kija tjazhinensis sp. n. St. Tyazhin, borehole 3, depth 403–410. Tyazhin Formation. Holotype. ×3.

Fig. 21. Kija miroschnichenkii sp. n. Tyazhin, borehole 3, depth 403–410. Tyazhin Formation. Holotype. ×2.3.

Fig. 22. Kija kibetenensis sp. n. Kibeten mulda, borehole 831, depth 163–167. Tyazhin Formation. Holotype. ×2.

Fig. 23. Naiadites krasnojarskiensis sp. n. Left bank of the Yenisei, 2 km upstream from the village of Barabanovo. Upper subformation of the Itat Formation. External mold. Holotype. ×2.

Plate 1

Plate II

Plate III