This genus has the ligament partially inserted internally, and has no
exterior angular groove. The valves never gape, often have rayed
longitudinal ribs, are compressed, and the shell by age becomes thick
and ponderous, sometimes attaining a large size. The teeth in the hinge
are not so numerous as in the Arca and Cucullæa; the centre teeth appear
worn down.
Shell close, orbicular, doubly convex, equivalve, sub-equilateral;
summits almost vertical, and more or less distant; hinge formed on each
valve by a rather numerous series of small teeth, disposed in a curved
line, sometimes broken under the summit; ligament external and large.
Pectunculus glycimeris.
P. pilosus.
P. undulatus.
P. marmoratus.
P. scriptus.
P. angulatus
P. stellatus.
P. pallens.
P. violacescens.
P. zonalis.
P. pennaceus.
P. rubens.
P. castaneus.
P. pectiniformis.
P. striatularis.
P. nummarius.
P. pectinatus.
P. radians.
P. vitreus.
_P. glycimeris._ The delicious Pectunculus.
Sub-orbicular, umbones produced; finely striated transversely and
longitudinally; covered with epidermis, under which it is marked with
reddish chestnut spots or bands; inside white; margins crenulated.
_P. pilosus._ The hairy Pectunculus.
Species convex, more or less smooth and hairy.
_P. pectiniformis._ The Pecten-shaped Pectunculus. Pl. 11, fig. 6.
Species lenticular, more compressed, pectinated, and more or less rough.