(Eydoux and Souleyet, Ms.) Gray, 1850
Diagnosis: Shell very broad, regularly curved dorsally, roughly triangular in outline, oval in cross-section, transparent, dark purple-brown body visible through wall. Sharp lateral ridges concave. Width near shell aperture about 3/4 total shell length. Lateral sides rounded in cross section. Three dorsal ribs present, medio-dorsal rib broadest, ventral side without ribs or swellings. Wavy transverse striation on ventral and dorsal sides, growth lines faint. Blunt ending, obtuse embryonic shell with transverse and longitudinal striae, not clearly delimited from teleoconch. Constriction between protoconch I and II absent. Shell length 19 mm, width up to 16 mm.