Diagnosis: Shell straight except for posterior section which curves abruptly dorsally, transparent, triangular in outline, oval in cross-section, dark body and visceral mass visible through wall. Lateral ribs well-developed, straight, regularly diverging, not excavated; longitudinal ribs on dorsal and ventral sides and transverse striation faint or absent, both sides flattened. Aperture width about one half to one third total shell length. Embryonic shell spherical without terminal cusp, separated from rest of shell by clear constriction. Shell length 20 mm, 5 times as long as broad.