A study of Hypoturrilites (Anmonoidea) from Hokkaido (Studies of the Cretaceous ammonites from Hokkaido and Sakhalin-XCI)

Abstract

This paper presents the result of our study on the genus Hypoturrilites from the Mikasa district, Central Hokkaido. H. gravesianus (d'Orbigny, 1842), H. wrighti sp. nov., H. komotai (Yabe, 1904), H. yabei Collignon, 1964 and H. nodiferus (Crick, 1907) are described, giving new or revised diagnoses and comparisons with other species. As to H. komotai the ambiguities in the previous record of occurrence are cleared up. Hence, the described species are all early Cenomanian in age. Finally the systematic allocation of Hypoturrilites in the Turrilitidae is discussed.