(Baird, 1850a)
Description:
Anterior margin of each valve with a thickened rim bearing two concentric carinae which are entire anterodorsally and discontinuous, giving way to spines, anteroventrally; outer (i.e., closest to margin) carina extends dorsally past eye tubercle in left valve only. Posterior margin rounded, bearing five or six prominent spines. A single spine at the posterodorsal corner is more prominent in the left valve. Distal process of male copulatory appendage elongate, subtriangular, with a concave anterior side and a rounded distal corner.
Habitat:
A common, sublittoral species, found as deep as 200metres but more usually in shallower water.
Remarks:
Many records of P. jonesii from the Mediterranean are referable to P. siveteri Athersuch, 1978a; this species differs from P. jonesii mainly in having a spinose but not carinate anterior margin. British records of P. siveteri are sub-Recent, and there are, as yet, no live records outside the Mediterranean.
Distribution:
British coasts, the Kattegat and the Skagerrak, French and Spanish coasts, the Mediterranean and the Black Sea.