SOME DIFFICULTIES IN RECOGNITION OF SEXUAL DIMORPHISM IN JURASSIC PERISPHINCTIDS (AMMONOIDEA)

Abstract.- The recent studies on perisphinctids have shown repeated occurrence of peristomal modifications and thus their limited reliability as a sign of ceasing of shell growth. Moreover, they have shown a trend to disappearance of the lappets at larger shell diameters. New evidence for the occurrence of the lappets on small-sized "macroconchs " is given and the transition from "micro- " to "macroconchs " seems possible. It is concluded that the perisphinctids may represent a new type of dimor-phism not encountered in other groups of ammonites and that the Makowski-Callo-mon hypothesis of the sexual dimorphism is not so universal as it was considered to be. The criterion of identity of inner whorls may be applied in the systematics of ammonites without making reference to the dimorphism as it was applied by Neumayr (1873) and Siemiradzki (1891)