Craspeditidae (Ammonoidea) of the Russian Platform at the Jurassic-Cretaceous Boundary. I. Genus Praesurites Mesezhnikov et Alekseev

The type species of the genus Praesurites,P. elegans Mesezhnikov et Alekseev, was described from the basal Berriasian of the Subpolar Urals (Sosva River basin). Finds of species of this genus in other regions are of importance for the interregional correlation of the Jurassic-Cretaceous boundary interval. The taxonomic composition and stratigraphic distribution of the Central Russian species of the genus Praesurites from the Volgian-Ryazanian boundary interval (the top of Craspedites nodiger Zone-Riasanites rjasanensis Zone) are revised. The revised diagnosis of the genus Praesurites and redescriptions of P. tryptychus (Nikitin), P. unshensis (Nikitin) (including P. nikitini Gerasimov et Mitta, as a junior subjective synonym) and P. craspeditoides (Girmounski) are presented.