Scallop, a bivalve of the genus pecten (Tur-ton), having the shell rounded, inequivalve, eared, with the upper margin straight and the hinge without teeth. The lobes of the mantle are widely separated, and include a glandular sac containing a gaseous fluid which enables the light shell to float easily and to change position with the tide; the mantle is reflected in a sub-marginal fold provided with tentacles, with numerous ocelli or eye spots near the margin. The mouth is jawless and toothless, with a tentacular labial border, the tentacles being short and separate from the branchiae; they have only one adductor muscle; the foot is long and cylindrical; the branchiae are disunited on the median line. They rest on the right side; some of the family attach themselves by a byssus, especially when young, but most are free, living on the bottom of the sea at moderate depths, moving by means of the hatchet-shaped foot and the recoil produced by suddenly opening and shutting the valves. In the common scallop (P. concentricus, Say) the shell is orbicular, the valves convex and nearly closed, with about 20 rounded ribs; it is dusky horn-colored, with alternating lighter and darker zones; the interior is shining white tinged with purplish, and grooved to correspond to the external ribs; the length and height are about 2 1/2 in., and the breadth 1 in.
It is abundant about the extremity of Cape Cod, whence it extends southward, being very common on the New Jersey coast; it varies considerably in color, with different degrees of whitish, reddish, and purplish; it is often handsomely zoned, and was formerly much employed for making card racks, pin cushions, etc. The muscle of the shell forms a delicate article of food. The P. Islandicus (Chemn.) is another American species, larger, handsomer, redder, with more numerous ribs, and living more to the north; it is found on the banks of Newfoundland, where it is a favorite food of many fishes, especially the cod. Some of the foreign species are very handsome, as the P. pallium (Lam.), or the duke's mantle, finely mottled with deep red; this is from the Indian seas. The more northern P. Japonicus (Gmel.) is also a beautiful reddish shell, though it varies much. A large species, P. maximus (Lam.), is common on the English coast in from 30 to 40 fathoms; the deeper shell was formerly used for scalloping oysters, giving the name to this favorite dish, and as a drinking cup.
The scallop of St. James (P. Jacoboeus, Lam.) is common in the Mediterranean, and was worn by pilgrims to the Holy Land.
Scallop (Pecten Islandicus).