Mussel, Or Muscle (Lat. musculus; Ger. Mu-schel), a well known lamellibranchiate mollusk of the genus mytilus (Linn.). It belongs to the dimyarian group, or those having two adductor muscles, the anterior being small; the mantle has a distinct anal orifice; the foot is small, cylindrical, grooved, with many retractile muscles and a large silky byssus divided to its base; the shell is longitudinal and subtri-angular, with the beaks terminal and pointed, dark-colored and shining. The common saltwater mussel (M. edulis, Linn.) is from 1 to 2½ in. long and 1 in. broad, of a greenish black color externally and purplish and bluish white within. This species is esteemed as food in Europe; they lie together in large beds uncovered at low water, and are more easily obtained than the oyster; they are most esteemed in autumn, as in the spring or spawning season they are apt to disarrange delicate stomachs and to produce a cutaneous eruption; thousands of bushels are annually obtained for food and bait for deep-sea fisheries, affording employment for hundreds of women and children, especially along the frith of Forth; they anchor themselves very firmly to rocks and stones by the horny threads of the byssus, directed by means of the foot, and attached by their broad disk-shaped extremities.

The common mussel of New England (M. oorealis, Lam.), by some considered the same as the last species, is eaten, fresh and pickled, in some parts of the country, but is more commonly used for bait or manure. The forms of their shells are very various, from accidental distortions or from the shape of the cavities and crevices in which they are commonly wedged. Several other species are described. - Another shell, commonly called mussel by the fishermen, is the allied genus modiola (Lam.), known in Europe as the horse mussel. Our common species (AT. modiolus, Turton) is from 4½ to 6 in. long and from 2½ to 3 in. wide; the shell is thick, coarse, and rough, with the beaks sub-terminal; the color externally is chestnut or dark brown-pearly within. It inhabits deep water, attaching itsellf very firmly to rocks, from which it is torn in great numbers during violent storms; it is almost always more or less distorted, and has seaweed or some parasite attached to it; though too tough for food, it makes excellent bait for cod and other deep-sea fishes, but is very difficult to obtain when wanted.

Other species live in brackish water; some in Europe are said to burrow and make a nest of sand and fragments of shells. - The fresh-water mussel (anodori) and river mussel (unio) are dimyarians, with a large foot not byssiferous in the adult; the hinge is toothed. The A. fluviatilis (Gould) has a thin, inequilateral shell, grassy green externally and lilac-tinted white within, and attains a length of 4½ in.; it is common in mill ponds and sluggish streams. Many other species of this genus, and of unio and allied genera in North America, have been specially described by Mr. Isaac Lea. Some of the unios, both in this country and in Europe, produce very fine pearls, and about 20 years ago there was a general pearl hunting in many parts of the United States, which resulted in the finding of a few valuable specimens after an immense amount of generally unprofitable labor. The pearl mussel of Europe (IT. margaritifera, Linn.) has long been famous for the ornamental excretions found in its shell, some of which are of rare beauty.

Common Salt-water Mussel (Mytilus edulis).