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Shell relatively thin but solid, inflated, inequilateral, roughly quadrate to subtrigonal in shape, with a rounded umbono-ventral keel and an obliquely truncated posterior margin; slightly inequivalve, left valve somewhat projecting beyond right along posterior and ventral margins. Umbones subcentral, prominent, on top of a well-developed trigonal cardinal area which is engraved by oblique, chevron-shaped grooves and covered with a black external ligament. Outer sculpture of numerous radial riblets and concentric threads forming a fine reticulation. Periostracum conspicuous, velvety. Hinge elongate, straightish dorsally and weakly arched ventrally, bearing a series of transverse, diverging outward teeth, and rather long, subhorizontal teeth at both ends, at least in adults. Interior of shell porcelaneous. Two subequal adductor muscle scars; inner margin of posterior scar on a projecting shelf. Pallial line without a sinus. Internal margins with a fine crenulation becoming obsolete in old individuals. Colour: outside of shell purple tan, with a yellowish periostracum. Inner side white, more or less strongly tinged with dark reddish brown posteriorly. |
