Elongated, equivalve, very inequilateral, polished with periostraeum extending fringe-like far beyond the margins of the valves; colour dark-brown, and lighter for a considerable area around the umbos, and faint concentric narrow bands; sculpture of very low broad and flat ribs radiating from the umbos toward the margins, interstices narrow, shallow, umbos very low, inconspicuous, at about the posterior fourth of length; anterior end broadly rounded, dorsal margin straight; posterior end rounded; ventral margin straight, parallel to the dorsal; periostraeum polished, brown horny, exceeding the valves, usually slit at the termination of a rib; margins inside thin and sharp; hinge without teeth, a dental callosity acutely produced toward the posterior side of each valve, margining the upper part of the posterior adductor scar, and a stout callous rib, becoming gradually thinner, almost encircles the adductor scar; ligament amphidetic, parivincular, internal, posterior, narrow; posterior position of ligament much thicker; interior of valves greyish-white, not iridescent; anterior adductor scar the larger, somewhat pear-shaped; pallial line not very distinct. Length 57 mm., height 26 mm., section 12mm. Type locality: King George Sound, Western Australia.