Shell white, small to medium-sized, inequivalve (right valve more convex than left valve), inequilateral (anterior usually less developped than posterior, and more rounded), with an irregular commarginal sculpture and a granulated microsculpture. The outline can be very distorted in crevice-nesting specimens but, when the animal is not constrained in its development by some obstacles, the valves are regular, with only some chips in the fragile margins.

« In the broader specimens the hinge is placed nearer to the larger end; such are not in general so uneven and rugose as those of a more sub-orbicular shape; but all are more or less sinuous and indented at the margins. Inside white; hinge furnished with a broad sub-triangular tooth in each valve… » – G. Montagu: Testacea Britannica part I, London 1803, p.43.