CHAMA.
ARCA.
OSTREA.
"Chama. Shell thick; hinge with a thick tooth, sometimes crenate, obliquely inserted into a corresponding channel. ([Plate 5.]) The shells of this genus vary greatly, which you will perceive upon comparing C. gigas and C. cor. (See [Plate 9], Isocardia cor.) The Chama genus is usually ribbed, foliated, or scaly. C. Lazarus is a beautiful species: C. cor is a British species, and the only one. The whole number is twenty-five.
"Here is Noah's-ark, an example of the genus Arca, and is found on our own coasts. The long hinge beset with sharp teeth, inserted into each other, renders the genus sufficiently marked; but in some species the hinge is curved. The form varies exceedingly. The number of species is forty-five. ([Plate 5.])
"Ostrea. In this well-known genus we lose sight of the toothed hinge. Take that Pecten, or scallop, which belongs to one division of Ostrea in this system, and tell me what holds the valves together. Charles is silent; what says Lucy?"
"Here are the remains of the same kind of substance which we saw in Donax and in Venus. I think it is called the ligament."
Plate 5.
Page 26.
