1) Cambrian and Ordovician Gastropoda

As the earliest fossiliferous strata so far known in the Japanese islands are Silurian, all the Cambrian and Ordovician gastropods reviewed in the present article are from the Chosen Group in Korea. In the Korean peninsula this group is distributed in two sedimentary areas: one is the "Heinan geosyncline" in North Korea, and the other is the "Yokusen geosyncline" in South Korea. Some 60 Cambro-Ordovician. Gastropoda and Monoplacophora were described in several faunal studies together with the rich tri-lobites, nautilolds, brachiopods and other fossils.

Of these molluscs, several Lower and Middle Cambrian species from the Chunghwa area of Pyongan-namdo in North Korea (Saito, 1936, Kobayashi, 1958b) and from the Mungyong (Bunkei) area of Kyongsang-bukdo in South Korea (Kobayashi, 1935) attract our special attention, because they represent such early primitive genera as Coreospira, Helcionella and Hampilina, which seem to be important for the consideration of the early history of molluscs.

Lower and Middle Ordovician gastropods occur more abundantly in the two sedimentary areas. Particularly in the Shorin, Bantatsu and Unkaku beds in Pyongan-namdo and Huanghae-do and the Chikunsan and Tsuibon beds of Kangwon-do, the Bellero-phontacea, Macluritacea, Euomphalacea and Pleurotomariacea are represented by many species (Kobayashi, 1930, 1931, 1934a, b, 1958b, etc.). According to Kobayashi, some of the gastropods are common or closely allied to the contemporaneous faunas in northeast and middle-south China, and further comparative studies are desired. Almost all the type specimens of these Cambro-Ordovician gastropods are preserved in the University Museum, University of Tokyo. Since each nominal species is represented by a relatively small number of specimens, we cannot always confirm the distinction between closely related species, but the scientific importance of this material must be emphasized.

2) Silurian and Devonian Gastropoda

In the Japanese islands the distribution of Silurian and Devonian sediments is restricted to a few narrow areas. Though some "bellerophontids," "pleurotomariids" and "murchisoniids" were reported to occur from the Silurian of west Shikoku and from the Devonian of north Honshu, no gastropods have ever been formally described.

3) Carboniferous and Permian Gastropoda

Carboniferous and Permian formations are widely distributed in many areas of Honshu, Shikoku and Kyushu. They commonly occur together and bear large limestone bodies at many places which sometimes yield well-preserved molluscan fossils. The most famous gastropod fauna comes from the Middle Permian Akasaka Limestone in central Honshu, where giant species of Bellerophon, Pleurotomaria [Bathrotomaria?], Naticopsis, Trachydomia [Trachyspira] and Murchisonia [Raha?] are known to have occurred at some quarries of Kinshozan.^* We owe their description and a number of fine drawing illustrations to Hayasaka (1938,1939, 1943), who is a pioneer of Paleozoic molluscan paleontol-ogy in this country. The unusually large size of the constituents of the Akasaka fauna was later discussed by Hayasaka and Hayasaka (1953), although there are also many other described or undescribed gastropods of small size at the same localities. While most of the type specimens of Akasaka gastropods are now believed to be preserved at the Taipei University of Taiwan (oral communication of Prof. M. Murata and Dr. T. Ozawa), some topotype specimens are at various museums and institutions in Japan. Besides, Hayasaka (1953) described a large specimen of Euconospira with original color pattern from the Middle Permian Nabeyama Limestone in Kwanto.

The Carboniferous-Permian Akiyoshi Limestone in west Honshu, which is also famous for its overturned geologic structure and exemplary fusulinacean zonation, bears some well-preserved gastropods, mainly in the lower part. Shikama and Nishida (1968) and Nishida (1968) recorded several interesting species belonging to Straparollus, Mourlonia and Twbonitella, which are almost the only described Carboniferous gastropods in this country. Furthermore, Nishida (1969) described a Middle Permian gastropod fauna from the Ohirayama Limestone in south Shikoku, which contained the genus Shikokuspira of the Neritopsidae and the subgenus Sorobanobaca of the Bellerophontidae.The secondarily silicified material of the Ohirayama fossils attracts our attention, suggesting the possibility of further ambitious investigation.

Many Carboniferous and Permian gastropod faunas from non-calcareous rocks seem to remain undescribed, since a considerable number of species have been listed in stratig-raphic papers. Only Murata (1969) described Euphemitopsis, Bellerophon, Straparollus, Glabrocingulum and a few other gastropods from the Upper Permian Toyoma Formation of north Honshu.

4) Triassic and Jurassic Gastropoda

In spite of a large number of described bivalve species from the Triassic and Jurassic of Japan, studies on the gastropod faunas are few and quite sporadic. The Upper Jurassic limestones of Torinosu type in north Honshu (Abukuma mountains), south Shikoku and middle Kyushu yield some nerineaceans. While a species and a subspecies of Nerinea were treated by Sugiyama and Asao (1942), most Jurassic nerineaceans, including Nerinea, Cossmannea, Ptygmatis, Cryptoplocus, Bactroptyxis, Itieria and Phaneroptyxis in addition to the genus, Heteroptygmatis, were described by Shikama and Yui (1973) together with some Lower Cretaceous species. Their classification of this superfamily seems to follow Pcelincev and Korobkov's scheme in Orlov (1960, ed.), which is considered controversial by other authors.

We are aware of the presence of many undescribed gastropods in the Triassic and Jurassic non-calcareous marine sediments, but only a few species were paleontologically described except for some pleurotomariaceans from the Middle Triassic Rifu Formation of north Honshu (Hayasaka, 1966) and some Neritopsis species from the Lower Jurassic Toyora Group in west Honshu (Hayami, 1960). From the lower and middle parts of the Tetori Group in central Honshu (Hida mountains), which is mainly Jurassic but possibly Lower Cretaceous in part, Kobayashi and Suzuki (1937) described Pila [Ampullaria?] and some other non-marine forms.

5) Cretaceous Gastropoda

The Upper Cretaceous deposits of Saghalin and Hokkaido contain numerous well- preserved molluscan fossils, offering world-famous fossil records (Matsumoto, 1954, etc.). Pioneer studies on the gastropod faunas in this region as well as the rich ammonites and inoceramids date back to the last century. Schmidt (1873) first described a huge patel-liform species of Helcion ["Capulus"] together with two species of Trachytriton [Serri-fusus?] from the environs of Alexandrovsk in north Saghalin. Yokoyama's (1890) and Jimbo's (1894) papers on many Cretaceous fossils mainly from Hokkaido and Neumayr's study in Naumann and Neumayr (1890) on Jurassic and Lower Cretaceous fossils from Shikoku and Kyushu also include descriptions of some gastropods. All the plates in these classical monographs were later reproduced with revised taxonomic remarks (Matsumoto, Hayami and Asano, 1963; Matsumoto, 1963; Hayami, Matsumoto and Asano, 1963).

During the 1920's and 1930's, Yabe and Nagao greatly contributed to the descriptions of Cretaceous bivalve and gastropod faunas in the Japanese islands. Yabe and Nagao (1925, 1928) reported many representative gastropods from the Upper Cretaceous of Saghalin and Hokkaido, and these works were followed by those by Nagao (1932, 1939) and Nagao and Otatume (1938). During the course of descriptive studies, Nagao proposed two interesting genera, Pseudogaleodea and Pseudoperissitys. Other common and characteristic genera of this epoch are Aporrhais (Tessarolax) and Pugnellus of the Strombacea and Serrifusus of the Buccinacea, which indicate some relation to the contempora-neous faunas of North America. Yabe and Nagao in Yabe, Nagao and Shimizu (1926) described Natica (Amauropsis) [Tylostoma?] and two other small gastropods from the Lower Cretaceous formations of the Kwanto mountains in central Honshu. Summarizing the Cretaceous stratigraphy of the Japanese islands, Yabe (1927) illustrated some Lower Cretaceous specimens of Purpuroidea, Tyiostoma and Glauconia [Cassiope], introducing new specific names for them. Although no description was given in that paper, the names are regarded as available, because they were proposed before 1930, Furthermore, some indigenous Albian-Cenomanian gastropods from the Amakusa islands of Kyushu were described by Nagao (1930) and Matsumoto (1938).

Nagao (1934) made an intensive study on the Aptian (partly Albian) gastropods from the Miyako Group in north Honshu. Indeed, this material seems to represent one of the most prolific gastropod faunas of this stage in the world. He described 28 species belonging to 22 genera, e.g., Ataphrus, Desmieria [Otostoma], Pseudomelania, Trajanella, Tyiostoma, Cerithium [Cirsocerithium, Cimolithium, Metacerithium], Bathraspira, Vani-koroa [Gyrodes], Avellana and Nerinea. Twenty-two of these species are entirely new, and subsequently Allison (1955) compared some specimens from the Albian of Baja California of Mexico with the Miyako species. One of us (T. K.) is now engaging in a further study on the Miyako fauna and has already distinguished more than 20 undescribed gastropods. Since the preservation of the material is exceptional, taxonomic and other studies on these gastropods may be significant beyond the description of a local fauna. Most of Yabe and Nagao's type specimens of the Cretaceous gastropods are now preserved in the Institute of Geology and Paleontology, Tohoku University, and the Department of Geology and Mineralogy, Hokkaido University, and were observed by us for the preparation of this catalogue.

In contrast with marine deposits, the distribution of Cretaceous non-marine formations with fossil gastropods is almost restricted to the Inner Zone of Southwest Japan and the southern part of South Korea. Since Kobayashi and Suzuki (1936) described non-marine molluscs including a new species of Brotia [Brotiopsis], a number of fresh-water and brackish-water gastropods belonging to Cyclophoracea, Rissoacea and Cerithiacea have been described from the Toyonishi and Kwanmon Groups in west Honshu and north Kyushu and from the Naktong and Shiragi Groups in Kyongsang-namdo and Kyongsang-bukdo of South Korea (Kobayashi and Suzuki, 1939; Suzuki, 1940, 1943; etc.). Although many subsequent Japanese stratigraphers and paleontologists havebeen more interested in some peculiarly ornamented unionoid bivalves rather than gastropods, there are such interesting indigenous genera as Itomelania, Brotiopsis and Siragimelania. Unfortunately, many of the original specimens treated by Suzuki were lost during the Second World War. After the war Ota (1960) and Hase (1960) additionally described non-marine gastropod faunas of the Kwanmon Group in west Honshu and north Kyushu and the Kawaguchi Formation in middle Kyushu. The former author proposed Yoshimonia and Kumania as two new subgenera of Melanoides.

Nakazawa and Murata (1966) described a new molluscan fauna including some species of gastropods from the Lower Cretaceous (probably Neocomian) Kamihei Group of north Honshu (Kitakami mountains).

In addition to Nagao's (1934) description of a species of Nerinea from the Miyako Group, Fukada (1953) described another large nerineacean from the Lower Cretaceous Lower Yezo Group of Hokkaido, and Tsuchi and Kagami (1967) reported the occurrence of valuable specimens of "Nerinea", which were dredged from the top of Seamount Erimo off the southern coast of Hokkaido. As noted before, Shikama and Yui (1973) accomplished a comprehensive study on the nerineaceans from Japan, in which some species of Nerinea and Phaneroptyxis from the Neocomian Oshima Formation in north Honshu (Kitakami mountains) were described together with the above-mentioned Miyako and Lower Yezo species. Another unique and special taxonomic study was recently completed by Kanie (1975), in which five patelliform gastropods were collectively redescribed on the basis of many specimens from Japan and Saghalin. He regarded these species as belonging to the genus Anisomyon and proposed the Anisomyonidae as a new family of the Calyptraeacea, transferring the genus from the Basommatophora to the Mesogastropoda. The presence of such large capulid gastropods is quite notable, though the generic assignment is, we think, still controversial.

* In this historical review revised generic names are shown in brackets immediately after the original names.[return to the text]