264 MOLLUSCA. 



triangular valves. One of the sides of the acute angle forms the hinge, and 

 is furnished with a long, narrow ligament. The head of the animal is in the 

 acute angle ; the other side of the shell, which is the longest, is the anterior 

 one, and allows the passage of the byssus ; it terminates in a rounded angle, 

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

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

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

 the water enters required for respiration. Before, and near the acute angle, is 

 a small transverse muscle, and a large one behind, near the obtuse angle. Its 

 foot resembles a tongue. 



Myt. edulis, Lin. Thy 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, Bruguicres, 



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, LIMNA:A, Poli, has no byssus ; its foot, which is very large, com- 

 pressed 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, Mylilus ci/ifneus, is 

 common in ponds, &c., 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, Bruguieres. 



These Mollusca resemble the Anodontea; both in their animal and shell, 

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

 cavity 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 which is inserted between 

 two others on the opposite side. They also inhabit fresh water, preferring 

 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 hinge, 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 



CARDITA, Biiiguiitres, 



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

 gaping. 



