Length 4.1 mm. Growth lines (1) may be visible on the valves.
When an intermediate valve is viewed from the posterior, it has a low, smooth, curved profile with a very slight keel (2).
Lateral (3) and pleural areas (4) are slightly differentiated by the slight elevation of the lateral triangle and the difference in orientation of granules.
Dorset, England. February 2018. Leg. S. Trewhella.