Description.—Specimen consisting of the natural cast of a left valve: form oblong, subtrigonal, mostly compressed; umbo anterior, depressed, incurved, succeeded in front by prominent lunuloid cavity; dorsal margin posteriorly elongate, oblique, continuous with the terminal curvature of margin; anterior region short, deep, slightly inflated on the ventral side of umbonal area; outer margin deeply excavated beneath the umbo, afterwards of oval contour; ventral margin anteriorly inflated, deeply sinuated in rear; posterior region furnished with an obtuse ridge directed obliquely from the umbo to the postero-ventral angle, on each side of which the valve slopes and becomes compressed; lateral face of valve between the anterior inflation and posterior ridge triangularly depressed; sculpture lines obscure.