1986 Volume 1986 Issue 143 Pages 463-474_1
Neocrioceras spinigerum (Jimbo), the type species of Neocrioceras, is redefined on the basis of the specimens in our collections as well as the hitherto described ones. Its adult body-chamber is spirally coiled in the same way as the phragmocone. It is quadrituberculate at intervals and the disposition of the ventrolateral tubercles is variable (opposite or alternate or irregular) among individuals and also with growth-stages. The quadrilobate suture is florid; I trifid and as deep as U; other elements bifid and of dove-tail form. Reliable records show that this species occurs in the Santonian of Hokkaido and Sakhalin. Comparison with other species is described at length, with a result that certain species previously referred to Neocrioceras should be transferred to other genera. In an appendix the genus Neocrioceras is redefined and its relationships with other genera are discussed.
