(Linné, 1758)
Description:
Shell very thin and delicate, approximately circular, almost flat. Left valve only slightly convex, umbo distinct, forming a short cone; inner surface smooth; oval, dorsal byssal scar and ventral adductor scar closely adpressed, slender, obliquely orientated, with smooth surfaces. Right valve very thin, translucent. Both valves with numerous, fine, concentric lines, visible with hand lens (H. squamula-drawing).
Size:
Up to 15 mm long, usually much less.
Colour:
Off-white, inner surface white.
Habitat:
On hard substrata and algae.
Distribution:
Ranges from Arctic waters south to the Bay of Biscay (Distr. H. squamula).