FRESHWATER MUSCLE, a popular name common to a whole family of lamellibran chiate mollusks, unionida (sometimes called naiada), allied to muscles (mytilida); but having a much larger foot,,,which does not generally produce a byssus (q.v.), except in a very young state of the animal. All the known mollusks of this family are inhabitants of fresh water, some of them being found in still, and some in running waters. A few species are European; but it is in North America that they chiefly abound, its. lakes and rivers producing many species. They crawl about by means of the foot; many of them generally live immersed in mud. They are supposed to feed on animalcules, and on decomposed animal and vegetable matter. The epidermis of many is brilliantly colored, and the inside of the shell is lined with a brilliantly and variously colored nacre, so abundant as to be sometimes used for mother-of-pearl. Pearls are sometimes pro duced. There are four British species, of which anodon eygneus, attaining a size of 21 in. long by 6 broad, is common in lakes, ponds, and muddy rivers. It is very varia ble in the thickness of the shell and in other particulars. The hinge is toothless. Two
species are confined chiefly to the s. and e. of England; the fourth (unto or alasmodon margarileyera, mya margaritifera of Linnaeus) inhabits the rivers of mountainous and hilly districts with a rocky bed, and has long been celebrated for the pearls which it produces. It is about 21 in. long by 5 broad, and has a thick blackish-brown shell, with a toothed hinge. It is the most northern European species, and is found in the rivers of Norway and Sweden. The pearls of the British rivers were famous among the ancient Romans; and Suetonius represents them as having formed an inducement for Caesar's expedition. Some of the rivers of 'Wales, the n.w. of England and Scotland, have at various times produced beautiful and valuable pearls. In several of the rivers and lochs in Perthshire, muscle-gathering is quite a trade, and the pearls found form the means of subsistence to many families. A pearl from the Conway, presented by sir Richard Wynn to the queen of Charles II., is among the ornaments of the British crown. Large and fine pearls have also been procured from rivers of Tyrone and Donegal.