ACEPHALA TESTACEA. 277 



and the third side ascends towards tlie hinge, to which it is joined by an 

 obtuse angle. The animal — Callitkiche, Poli, has the edges of its mantle 

 provided with branched tentacula near the rounded angle, as it is there that 

 the water enters requu-ed for respiration. Before, and near the acute an- 

 gle is a small transverse muscle, and a large one behind, near the obtuse 

 angle. Its foot resembles a tongue. 



Myt. edulis, L. This common Muscle is frequently seen suspended in 

 extended clusters, along the whole coast of France, to rocks, piles, &c. &c. 

 It forms a considerable item of food, but is dangerous if eaten to excess. 



Some of them are found fossil. In the 



Anodontea, Brug. 



The anterior angle rounded like the posterior; the hinge of the thin and 

 moderately convex shell has no appearance of a tooth whatever, being 

 merely furnished with a ligament which extends along the whole of its 

 length. The animal, — Limn^a, Poli, has no byssus; its foot, which is very 

 large, compressed and quadrangular, enables it to crawl upon the sand or 

 ooze. The posterior extremity of its mantle is provided with numerous 

 small tentacula. The Anodontes inhabit fresh water. 



Several species are found in France, one of which — Mytilus cygneus, is 

 common in ponds. Sec, with oozy bottoms. Its light and thin shells are 

 used for milk-skimmers, but its flesh is not eaten on account of its insipidity. 



Unio, Brug. 

 These MoUusca resemble the Anodontese both in their animal and shell, with 

 the exception of their hinge, which is more complex. There is a short ca- 

 vity in the anterior part of the right valve, which receives a short plate or 

 tooth from the left one, and behind it is a long plate wliich is inserted be- 

 tween two others on the opposite side. They also inhabit fresh water, pre- 

 ferring running streams. 



Numerous species, remarkable for size or form, inhabit the rivers and 

 lakes of the United States. Messrs Say and Barnes, who have described 

 them, have established some new subgenera among them. 



There are certain Marine Mollusca which have a similar animal, and about 

 the same kind of liinge, that should be placed near the Unios; the summits 

 of the shell, however, are more convex, and it is marked by projecting ribs 

 extending from the summits to the edge. They form the 



Caedita^ Brug. 

 "Which are more or less oblong or codlform, the inferior margin, in some, 

 gaping. 



CypRiCARDiA, Lam. 



Cardltac, in which the tooth under the summit is divided into two or three. 

 Their form is oblong, and their sides unequal. 



