"Very well remembered," continued her father. "The generic character of this very large portion of bivalves is, shell bivalve, usually with unequal valves: hinge without teeth, having a hollow cavity or sinus, and sometimes grooved. Here is a young common oyster, and, according to the rule of our present system, this shell, Ostrea isognomon, is of the same genus. ([Plate 5.]) The number of species is eighty-four, of which thirteen are British. The old shells of common oysters are often covered with Serpula, Lepas, and Anomia, and some kinds of corallines.
ANOMIA.
MYTILUS.
"The next genus, Anomia, is remarkable for the thin, delicate, and almost transparent appearance of the shells. The valves are unequal, and frequently perforated near the apex; hinge toothless; in the flat valve, two bony rays.
"Anomia ephippium has a large perforation, through which the animal passes a ligament, and attaches itself to other substances. These shells are often to be found on oysters. ([Plate 5.]) Species thirty-two.
"Mytilus. The principal characters are, shell bivalve, rough, often affixed by a thick byssus, or beard; hinge without teeth, with a hollow line extending lengthways. ([Plate 3.])
"The common muscle, Mytilus edulis, must be well-known to you, and also the fine polish that the shells will take when cleared of the rough exterior by artificial means, Mytilus barbatus is not unfrequent on our shores; the colour is brown, and the shell is shaggy. Number of species, forty-nine.
PINNA.
"Our last bivalve genus is Pinna. The generic characters—shell bivalve, brittle, erect, gaping at one end, throwing out a byssus; hinge without teeth. ([Plate 6.])
"The Pinna race are found plentifully in the Mediterranean, the Indian, American, and Atlantic oceans: the British seas afford three species. The genus is noted for producing a fine byssus, that is manufactured in Italy into various articles, as gloves. The animal is sometimes used as an article of food.