871. SOME INOCERAMIDS (BIVALVIA) FROM THE CENOMANIAN (CRETACEOUS) OF JAPAN-V : A WORLD-WIDE SPECIES INOCERAMUS PICTUS SOWERBY FROM JAPAN

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  • 871. 本邦白亜系セノマニアン階産イノセラムス-V : 世界的分布種 Inoceramus pictus Sowerby の産出
  • 本邦白亜系セノマニアン階産イノセラムスー5-世界的分布種Inoceramus pictus Sowerbyの産出〔英文〕
  • ホンポウ ハクアケイ セノマニアン カイサン イノセラムス 5 セカイテキ ブ

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Abstract

Inoceramus pictus Sowerby is well known for its world-wide distribution in the upper part of the Cenomanian. For some reasons, however, no example of this species has been described from Japan. I. pictus is regarded as highly variable and currently divided into more than six subspecies. Some of them are reviewed in this paper for careful comparison with our forms. I have realized that some specimens of rather old collections from several localities in Hokkaido are referable to this species, although they are atypical. They are described in this paper under a new subspecies, which is distinguished from I. pictus pictus by its less distinctly marked growth striae, finer rings and weaker concentric subcostae and/or undulations, instead of pronounced major ribs or folds. The form from Kamchatka called "I. pictus neocaledonicus" by Pergament may be preferably transferred to this new subspecies.

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