| Diagnosis |
Shell reaching a large size, usually rather thin, fragile, moderately inflated and triangularly wedge-shaped in outline, with a highly variable sculpture. Dorsal margin nearly straight or slightly concave, posterior margin generally truncate. Ventral margin widely convex posteriorly, straightish to shallowly depressed anteriorly. Outer surface of valves with 15 to 30 radial ribs which may be smooth to densely set with short, open spines. Dorsal most radial rib frequently with a series of short and sharp spines protruding along the dorsal margin of shell. Inner surface of shell with shallow grooves corresponding to the external radial ribs. Internal nacreous layer rather thin, undivided, occupying the anterior 2/3 to 3/4 of valves. Posterior adductor scar completely enclosed within the nacreous area. Colour: outside of shell slightly shiny, translucent olivaceous tan, often tinged with darker purplish brown or grey toward the umbones. Interior similarly coloured, iridescent on nacreous area. |
