Disarticulated valves, dorsal view. Length when live 3.5 mm. The surface of the tegmentum (outer shell-layer) has large granules that vary from rounded bosses (1) to rough angular sculpture(2) .
On intermediate valves (ii to vii), the granules are largest near the anterior and lateral edges (3). Lateral (4) and pleural (5) areas are differentiated by the slight elevation of the lateral triangle and the difference in orientation of granules.
The head valve (i) is semicircular with a widely V-shaped posterior margin; its granules are largest near its curved edge (6).
Granules on the tail valve (viii) are largest near its entire periphery (1).
Lines of granules may be indistinct if the shell is worn or has adhering secretions or deposits. Growth lines may be visible on the valves.
Dorset, England. February 2018. Leg. S. Trewhella.