| Diagnose |
Shell rather small, thin and fragile, somewhat translucent, roughly elongate trapeziform in outline, with very long and rather narrow shape. Anterior margin of valves quite short and sharply rounded, clearly extending forwards beyond the umbones. Ventral margin very long and broadly concave medially. A broad and rounded keel, radiating obliquely towards posteroventral end of valves and bordered anteriorly by a wide and shallow depression determining the sinuation of ventral margin. Outer surface of valves smoothish with only fine concentric growth lines and a few small radial grooves in front of the umbones. Periostracum smooth and shiny, translucent, closely applied to shell surface. Hinge line with very small crenulations, mainly appearing behind the ligamental margin. Anterior adductor scar present. Internal margins very thin and smooth, undulate anteriorly in relation to the outer radial sculpture. Colour: outer coloration variable, light tan to olive-green or brown, often paler on the keel, with a median radial band and sometimes irregular transverse stripes of purplish brown on posterodorsal slope. Interior slightly pearly, pale bluish grey with the outer colour pattern showing through. |