Ammonites of the Ryazanian Stage of the Russian Platform: Genus Pronjaites Sasonova

The ammonite species Olcostephanus bidevexus Bogoslowsky, 1896 and O. suprasubditus Bogoslowsky, 1896, established in the Ryazanian Horizon (=Stage) of the Oka River basin, are discussed based on study of their type series and new collections from the type locality. Both species characterize the middle part of the Ryazanian Stage (the lower and upper parts of the Spasskensis Zone respectively) and are attributed to the genus Pronjaites Sasonova, 1971, with the type species Olcostephanus bidevexus Bogoslowsky, 1896. The new species Pronjaitesyolkinensis sp. nov. is described from the uppermost lower Rjasanensis Zone. A single specimen assigned to the genus Pronjaites in open nomenclature is reported from the upper part of the Ryazanian Stage, in the Tzikwinianus Zone. An emended diagnosis of the genus Pronjaites is given.