757. CRETACEOUS NAUTILOIDS FROM HOKKAIDO-I

Abstract

I am going to monograph the Cretaceous nautiloids from Hokkaido on the available material in a series of papers, sometimes with coauthors. This paper contains, as Part 1, descriptions of three species from the Turonian and Coniacian of central Hokkaido. To describe two of them I establish a new genus (Kummeloceras) which is interpreted as a member of the root stock of the Nautilaceae derived directly from Cenoceras. In connexion with the establishment of the new genus, discussion is extended to the evaluation of the Eutrephoceratidae Miller, 1951 with necessary revision and the alteration of the concept of the Nautilidae, with Hercoglossidae Spath, 1927 as its synonymy. The three species are new but allied to certain previously known species outside Japan. The first species is similar to "Nautilus" splendens Blanford and occurs in the Middle Turonian. The second is allied to "Nautilus" fleuriausianus d'Orbigny and occurs in the Coniacian. They are referred to the new genus. The third is allied to "Nautilus" indicus d'Orbigny and is assigned to Eutrephoceras. It occurs in the Lower Turonian.