Shell moderately solid, elongate, nearly equilateral, left valve plane, right much compressed. Colour white. Dorsal margins nearly straight, meeting in a hook at the umbo. Posterior end broadly" and obliquely truncate, anterior angular. Sculpture: about ten concentric, graduated, broad and high corrugations, which are sharply bent on crossing an imaginary line between the umbo and the posterodorsal angle. In the left valve the crests of the ridges are acute, in the opposite valve rounded. A high magnification exhibits a secondary sculpture of dense minute grains arranged radially. Length 6 mm.; height 4 mm. Rare; a few separate valves from 17-20 fathoms.