In this part 66 named and 56 specifically unnamed Paleozoic Bivalvia which have been described or illustrated prior to 1976 on the basis of materials from Japan and Korea (Tables 3 and 4) are taxonomically treated. They are mostly Ordovician and Permian species, whose distribution seems to be restricted to this region. No descriptive studies have been attempted on Silurian and Devonian bivalves. Described Carboniferous bivalves are exceedingly few, though we are aware of the occurrence of a considerable number of species through various stratigraphic papers. As is clear from the marked difference in the numbers of descriptive works, research on Paleozoic bivalves is lag ging far behind that on Mesozoic and Cenozoic ones.

We owe our present knowledge about the Ordovician bivalves from Korea almost entirely to Kobayashi's (1931, 1934a, b) faunal studies. About 20 species were reported therein from the Chosen Group located mainly in the Taebaeksan area of South Korea. Most of them were referred to Ctenodonta and Modiolopsis, while Cyrtodonta?, Pterinea? and Goniophora were represented by one species each. It is worthy of note that three species of the Rostroconchia were described therefrom. These species are interesting in connection with the consideration of the major classification and early phylogeny of molluscs together with the Wanwanian species (Kobayashi, 1933) from northeast China, which were recently revised by Pojeta and Runnegar (1976). The main object of Ko bayashi's studies on the Cambro-Ordovician faunas of Korea, however, seems to have been the description of the trilobites and nautiloids, which are more abundant and strati graphically more important than the bivalves. Almost all of his described specimens of bivalves are now preserved in the University Museum, University of Tokyo, offering important data on the early history of this class. Yet, each nominal species is represented by only one or a few specimens, and regrettably we cannot always confirm the distinction between closely related species from the same localities. Only generic assignment of a few nominal species is altered, and the category and status of the type specimens are clarified in the present revision.

Research on Permian bivalve faunas in Japan was begun by Hayasaka in the 1920's. After describing several species from the Permian of the Kitakami mountains (north Honshu) in some short papers, Hayasaka (1925) published a monograph on one Carbon iferous and 12 Permian bivalves from the clastic rocks of Kitakami and the Akasaka Lime stone of Mino mountains (central Honshu). Specimens of Parallelodon, Aviculopecten [Hayasakapecten], Myophoria [Schisodus} and Solenomorpha [Alula] from Akasaka are exceptionally well preserved, cutting brilliant figures among Paleozoic molluscan fossils from Japan together with some associated giant gastropods. Ichikawa (1951) described a peculiar bivalve fauna from the Upper Permian Katsura Formation in south Shikoku. Among others the newly proposed genus Actinodontophora [type-species: A. katsurensis Ichikawa, 1951] seems to be quite important, because it was taken as the type genus of the family Actinodontophoridae Newell in Cox et al., 1969, and also because its hinge structure is informative about the phylogeny and hinge development of the subclass Praeheterodonta.

In recent years notable progress in research on Permian bivalves from this country has been achieved mainly through the efforts of Murata, Nakazawa and Newell. Naka zawa (1959, 1960) described some species of Bakevellia and the Myophoriidae from the Upper Permian Gujo Formation in the Oe area of central Honshu, together with many Lower Triassic species. Murata (1964) accomplished the description of the Middle Permian Aviculopectinidae from Kitakami, which show considerably greater specific diversity. Nakazawa and Newell (1968) surveyed all the hitherto known species of Per mian bivalves from Japan and described 58 species belonging to 39 genera on the basis of the newly obtained material from Kitakami and the Maizuru zone of central Honshu. The up-to-date classification of this class adopted in their paper is important, since it seems to add some information to the system of the Treatise which was published almost simultaneously. They proposed five new genera, namely, Towapteria [type-species : T. nipponica Nakazawa and Newell, 1968], Tambanella [type-species: T. gujoensis Nakazawa and Newell, 1968], Ensipteria [type-species: E. onukii Nakazawa and Newell, 1968], Hayasakapecten [type-species: H. shimizui Nakazawa and Newell, 1968] and Gujocardia [type-species: G. oviformis Nakazawa and Newell, 1968], and also one new subgenus, Permoperna [type-species: Waagenoperna (Permoperna) hayamii Nakazawa and Newell, 1968]. As noted by them, the Late Permian Gujo fauna seems to contain some Mesozoic elements, and the Permian bivalve fauna from Japan may offer significant data for the consideration of the Permian-Triassic transition as well as the inferred mass extinction of this age (Kanmera and Nakazawa, 1973; Nakazawa and Runnegar, 1973). Murata (1969, 1971) described some bivalves from the Upper Permian Toyoma Formation and the Lower Permian Sakamotozawa Formation of the Kitakami mountains, proposing a new genus, Pseudoactinodontophora [type-species: P. yabei Murata, 1971] from the latter formation.

Thus as many as 100 Permian bivalve species including many characteristic taxa have been described from Japan. Except for several species from the Akasaka Limestone, most specimens are external and internal moulds without original tests. Nevertheless, recent technical advancement of silicone rubber casting seems to have provided great facility for taxonomic studies and actually enabled us to examine the external and internal characters of the shells in detail.