94 CLASS ACEPHALA. 
GRYPHAA, Lam., 
Certain oysters, mostly fossil, of the ancient calcareous and 
schistose strata, in which the summit of the most convex 
valve greatly projects and curves more or less into a hook or 
portion of a spiral; the other valve is frequently concave. 
The greater number of these shells appear to have been free ; 
some of them, however, seem to have adhered to other bodies 
by their hook. | 
G. tricarinata. The only living species known. 
PECTEN, Brug., 
Very properly separated from the oysters by Bruguicéres, 
although they have the same kind of hinge. They are easily 
distinguished by their inequivalve semi-circular shell, almost 
always regularly marked with ribs, which radiate from the 
summit of each valve to the edge, and furnished with two 
angular productions called ears, which widen the sides of the 
hinge. The animal (ArGus, Poli) has but a small oval foot, 
placed on a cylindrical pedicle, before a sac-like abdomen 
that hangs between the gills. Some species, known by a 
deep emargination under their anterior ear, are furnished with 
a byssus; the others cannot adhere, and even swim with 
rapidity by suddenly closing their valves. The mantle is 
surrounded with two ranges of filaments, several of the exter- 
nal ones being terminated by a little greenish globule; the 
mouth has numerous branched tentacula, in place of the four 
usual labial leaflets. The shell is frequently tinged with the 
most lively colours. 
The great species of the French coast (Ostrea maxima, 
Linn.), has convex valves, one whitish and the other reddish, 
each having fourteen ribs, broad, and longitudinally striated. 
The animal is eaten. We may also remark the sole of the 
Indian Ocean (Ostvea solea), Chemn. VII. 1xi. 595, with ex- 
