Moderately inflated, thick obliquely truncate-oval, very inequilateral; covered with a thin, brown, glossy periostracum, which is raised into slender folds of growth; umbos prominent, inflated, approximate, inclined towards the front, nearly terminal; anterior oblique, narrowly arcuate, interrupted only beneath the hinge extremity by an inconspicuous byssal sinus; posterior side more arched and regularly rounded to the obliquely semi-circular ventral margin; dorsal outline straight; hinge line broad, transversely plicated at both ends, the plications interrupted by a ligamental groove, which descends obliquely from the umbo; about 20 plications on the anterior side, about 30 posteriorly; interior bluish-brown, glossy, with a paler or white clouding circumferentially; edge of valves slightly thickened, particularly in the post-dorsal margin, which is furnished with from four to six tooth-like crenatures, the terminations of the radial ridges. Holotype: length 2 mm., height 2 mm., section 1.5 mm. —in shell sand, MacDonnell Bay.

MacDonnell Bay to St. Francis Island, down to 200 fathoms. S.W.A., S.A., Tas., Vict.