A pachydiscid ammonite Lewesiceras from the Cenomanian of Japan Studies of the Cretaceous ammonites from Hokkaido and Sakhalin-XCVI.

A specimen of ammonite obtained by Toshio Shimanuki from the lower Cenomanian (Cretaceous) outcrop in the Hobetsu district of Hokkaido, northern Japan, represents a new species of Lewesiceras (Pachydiscidae). In as much as Cenomanian specimens hitherto reported under Lewesiceras have been too immature for precise generic assignment, the present specimen is large enough to reach the adult stage. It represents a new species of Lewesiceras, and shows in some respects a step in the evolutionary change of characters from late Albian Eopachydiscus to the typical Turonian species of Lewesiceras.(Contributed by Tatsuro MATSUMOTO, M. J. A., Sept. 12, 2003)