770. CRETACEOUS NAUTILOIDS FROM HOKKAIDO-III : PART 3. SOME NAUTILOIDS FROM THE CAMPANIAN OF SOYA, NORTHERN HOKKAIDO

Abstract

This is Part III of a monograph of the Cretaceous Nautiloids from Hokkaido being published in series. It contains the descriptions of the three species from the Campanian strata exposed on the northwestern coast of Cape Soya (Textfig.1). The first is a new species of Eutrephoceras, which is allied to E. kobayashi Matsumoto and E. pseudobouchardianum (Spengler) but its siphuncle is central instead of subventral or subdorsal. Its whorl is broader and more inflated than E. tawaense Furuichi or E. balchistanense (Spengler). The second is a new species of Cymatoceras, which resembles C. cenomanense (Schluter) but its suture is not so sinuous as in that species. The third is a new species of Anglonautilus, which is distinguished from A. undulatus (Sowerby) in its much weaker ribs and the development of a shallow ventral groove on its body-chamber. The group of strata in the studied area is subdivided into 8 members, A to G in ascending order, of which A to D are the Middle Campanian and E to G the Upper Campanian. The first species occurs in C and D, the second in F and the third probably in C. They are all of shallow open sea facies.