777. CRETACEOUS NAUTILOIDS FROM HOKKAIDO-V

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  • 777. 北海道産白亜紀オウムガイ類-V
  • 北海道産白亜紀オウムガイ類-5-〔英文〕
  • ホッカイドウサン ハクアキ オウムガイルイ 5 エイブン

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This paper contains Parts 5, 6 and 7 of the Cretaceous nautiloids from Hokkaido. Part 5 concerns with the species from the Lower Cretaceous. The descriptions are given under 3 sections by different coauthors. Section A by T. Matsumoto and T. Miyauchi is on Cymatoceras sp. aff. C. virgatum (Spengler) from the Albian of Oyubari and Soya, which differs from the holotype from India by less inflated whorl. Section B by T. Matsumoto, Y. Kanie and Y. Miyata is on Cymatoceras sp. cf. C. sakalavum Collignon from the Albian at a locality (Text-fig. 1) about 17km NNW of Urakawa. Section C by T. Matsumoto and Y. Ueda is on Cymatoceras sp. aff. C. mikado (Krenkel) from the Neocomian of Rebun Island, which resembles C. mikado from Tanzania but differs in having subtrapezoid instead of subcircular whorl section. Part 6 by T. Matsumoto is on an additional species from the Santonian of Ikushumbets based on T. Takahashi's collection. It is identified with Cymatoceras sharpei (Schluter), being especially similar to the Gosau form. Part 7 is a summary of results by T. Matsumoto. (1) The described 15 species are listed with the age of the original beds (see p.341). (2) The phylogeny of the Nautilidae is tentatively presented (Text-fig.4), showing the relationships of the newly established genus Kummeloceras with other revised genera. (3) In Hokkaido nautiloid species are different from a stage to another. Certain species are characteristic of a particular zone. Some are well correlated with the allied ones in extra-Japanese provinces. (4) Many nautiloid genera show world-wide distribution during the Cretaceous Period, but at specific level there are regional differences. This is exemplified also by the species from Japan. (5) Discussion is given on the palaeoenvironment on some species from Hokkaido.

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