Further notes on the ammonoid genus Parajaubertella

On the basis of additional material, a revised diagnosis of Parajaubertella kawakitana Matsumoto, 1943 is given and P. zizoh sp. nov. is established. While the former is fairly large, the latter is small. The globose shell, consisting of much depressed whorls with a deep and narrow umbilicus and a subangular umbilical edge, occurs for a while in the ontogenetic development of Parajaubertella. In P. kawakitana this character occurs in an early substage (shell diameter from 5mm to 35mm), and is followed by a long-continued middle stage, whereas in P. zizoh it appears somewhat later and extends to an early part of the adult body chamber. The adult body chamber is characterized by the bandlike or low, foldlike, broad ribs separated by narrow grooves (=adult sacya-type ornament) in both species. Their common ancestor, if any, has not been found. On the basis of the characters of the two species, Parajaubertella is referred to the Gaudryceratidae instead of the Tetragonitidae. The two species occur commonly in the Lower Cenomanian, but the level of their first appearance has yet to be investigated.