CLAM, the name applied to many bivalve molluscs (see LAMELLIBRANCHIA) from the vice-like firmness with which the shell closes. In Scotland the name is usually applied to the scal lop (q.v.), in England to species of Mya and Mactra especially the gaper, Mya truncate. In the United States the name has a wider use, but most commonly denotes Venus mercenaria, the quahog or hard clam, and Mya arenaria, the soft clam, both of which are of great importance as food, besides being extensively used by fishermen as bait. The hard clam is allied to the cockle (q.v.) and has a heavy shell which was used as shell-money (see WAMPUM) by the Indians. It is found in one to six fathoms of water off the Atlantic coast of North America from Florida to Cape Cod and also off New Brunswick. It is obtained by raking the bottom. Young specimens, known as "little necks," are sold in large numbers in New York. The soft clam is found mainly be tween the tide-marks and has a thin shell and long siphons. "Clam bakes," where clams are placed on heated stones with potatoes and other food, the whole being covered with sea-weed and left to cook, make a popular picnic in America. Atlantic clams have been transplanted to the Pacific coast of North America with great success, though there are several indigenous species there which are also known by this name. It is an interesting point that while both Mya and Mytilus (the sea mussel, q.v.) occur on both sides of the Atlantic, the former is not eaten in Europe, the latter not in America; furthermore, in the prehistoric "kitchen-middens," remains of Mytilus are found in Europe and of Mya in America, but not vice versa. The American "fresh-water clams" are fresh water mussels (Unionidae).
Of other species to which the name clam is applied, the most noteworthy are the bear's paw clam (Hippopus maculates) of the Indian ocean, with a beautiful ridged white shell, marked with spots of purplish-red; and the giant clam (Tridacna gigas) of the East Indies, the largest of all lamellibranchs; the actual animal may weigh 20 lb. and the shell nearly a of a ton.