Small, thin, obliquely oval, white; umbos central, inflated, projecting, approximate; hinge margin straight; dorsal area transversely elongate, narrowly triangular; anterior dorso-lateral angle obtuse, about 135 degrees; posterior about 100 degrees; anterior border at first slightly concave, then nearly straight; ventral border semi-circular; sculpture of 16 radial ribs, smooth, rounded, nearly as wide as the interspaces, with several intercalated riblets; concentric striae granulate the intercostal spaces, and form sublenticular costulae on the sides, more marked on the anterior, near the dorsal border; resilium subcentral, triangular, concave; hinge plate narrow near the resilifer, widest at the angles; teeth about seven on each side, diverging, extending slightly along the lateral borders; interior slightly furrowed by the ribs; ventral margin squarely denticulated. Holotype: length 3 mm, height 3.7 mm.—104 fathoms, 35 miles south-west of Neptune Islands. (Reg. No. D.13055, S.A. Mus.)
Loc.: Cape Jaffa to 90 miles west of Eucla, 50-140 fathoms. S.W.A, S.A.