(Gmelin, 1791)
Description (shell):
Shell is inequivalve, right (lower) valve is fragile, flat and left (upper) valve is thin and convex. The form of both valves can vary and be very irregular; approximately circular in outline. Byssal aperture is pear-shaped. Ligament pit is half-moonshaped. Sculpture of upper valve is very fine, concentric and radiating lines with minute scales present, where the shell has not been weathered, it is frequently encrusted; lower valve with fine concentric lines. Interior of left (upper) valve with radiating furrows on the adductor and byssal muscle scars, which are joined together to form one continuous scar. Lower valve with one adductor muscle scar (P. squama-drawing).
Size:
Up to 38 mm in diameter.
Colour:
Upper valve is dirty white or brown in colour; lower valve is translucent. Interior of upper valve is glossy, mostly dark green.
Habitat:
Prefers bottoms of coarse sand, gravel, stones and shells from low water mark to about 75 m living on other mollusc shells, (particularly scallops) rocks and stones.
Distribution:
Its distribution is difficult to assess but it may range from Norway south to the English Channel (Distr. P. squama).