Revision of Bathytormus (Crassatellidae, Bivalvia) of the Middle Eocene of Krivoi Rog (Ukraine)

The results of the revision of Crassatella (Bathytormus) species from Middle Eocene deposits exposed by the quarry of the Ingulets Mining and Processing Plant and Vizirka-1 quarry (town of Krivoi Rog) are presented. The genus Bathytormus has been reclassified as a subgenus. Forms with ridge-like ribs in the umbonal region were differentiated from the species previously described as Bathytormus cipitis cipitis (Berezovsky, 1998) and described as a new species, Crassatella (Bathytormus) ignava sp. nov. The name C. ( B. ) cipita is retained for valves in which the upper part is covered with spaced lamellar ribs. C. ( B. ) cipita and its nominotypical subspecies are redescribed due to changes in their composition and diagnostic features.