Original diagnosis :  Solid shell, thick and heavy; equivalve, inequilateral, strongly inflated and longer than high (maximum length 40 cm, commonly 20 cm). Umbo position is in midline. Outline of shell fan-shape; posterior and ventral margin meet at an angle less than 900 ; anterior and ventral margin meet an angle less than 900 ; posterioventral and anterioventral margin meet at an angle more than 900 . Hinge with 1 ridge-like cardinal tooth, 2 lateral teeth on right valve, 1 lateral tooth on left valve. Pallial line presence but no pallial sinus; 1 adductor muscle scar. Outer surface sculptured with 9 to 14 large radial fold with 2 to 3 small rib-like at each interstices; anteriodorsal margin with interlocking crenulations, byssal orifice presence on anteriodorsal area but without byssal gape. Inner margin with irregular crenulations correspond with the sculpture of outer surface. Coloration on outer surface whitish, irregular reddish blotches arranged in irregular concentric bands; inner surface porcelaneous white. Inhalent siphon without tentacles.