Shell rather large and solid, inflated, unilateral, in shape passing from trapezoidal when young to mussel-form in the adult. Umbo terminal, projecting, dorsal margin straight, posterior and ventral margins rounded, anterior side concave' above, convex below. Colour buff. Epidermis dense, persistent, developing about a dozen radiating rows of long dense bristles which project beyond the margin; between the rows the surface is closely latticed with transverse lamellae. Under the epidermis the surface of the valve is concentrically irregularly striated. Prodissoconch a simple semi-circular unsculptured plate slightly bulged. Ligament visible externally along half the dorsal margin. -Hinge with a single stout tuberculate tooth in the anterior extremity of the left valve, which is independent in youth, but in the adult coalesces with the margin of the valve." Beneath it is excavated in the hinge plate a broad shallow byssal chamber. All the inner margin of the valve is smooth. Height, 6 ; length, 4-5mm.