ACKI’HALA tkstacea. 
85 
O. fo/ium, L . ; Ib., Ixxi, 662, 666. Oval; the margin plicated 
in zig-zag ; it attaches itself by the indentations in the back of 
its convex valve to the branches of the Gorgoni;e and other 
Lithophytes*. 
M. de Lamarck separates by the name of 
Gryph.ea, Lam., 
Certain oysters, mostly fossil, of the ancient calcareous and schist- 
ous strata, in which the summit of the most convex valve gi'eatly 
projects and curves more or less into a hook, or is partially 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 hookf. 
G. tricarinata. The only living species known. 
Pecten, Brag., 
The Pectens, very properly separated from the Oysters by Bru- 
giere, although they have the same kind of hinge, are easily distin- 
guished by their inequivalve semi-circular shell, almost ahvays regu- 
larly 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, 
Poll, has but a small oval foot j; placed on a cylindrical pedicle be- 
fore a sac-like abdomen that hangs between the branchiae. Some 
species, known by a deep eniargination 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 sur- 
rounded with two ranges of filaments, several of the external ones 
being terminated by a little greenish globule. The mouth has nu- 
merous 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, L., 
has convex valves, one whitish, the other reddish, with fourteen 
ribs each, that arc broad and longitudinally striated. The 
animal is eaten. 
We may also remark the Sole of the Indian Ocean, Ostrea so- 
lea, Chemn., VII, Ixi, 595, with extremely thin and almost equal 
* The various species of Oysters, on account of their irregularity, are not easily 
distinguished : to this genus are referred the Ost. orbicularis ; — O. fornicafa ; — O. 
sinensis; — O. Forskahlii; — O. rostrata ; — O. cirginica ; — O. cornucopia; — O.senega- 
Icnsis ; — O. stellata; — O, ovalis ; — O.papyracea, and the Mi/Hlus crista-galli ; — M. 
hyotis; — Af. /roas, Gmel., and those figured by Brugiere in the Encyc. Method., 
pi. 179, 188. 
It is almost certain, however, that several of these pretended species are mere 
varieties. 
The Osi. semi-aurifa, Gualt., 8-1, H, is a young Acicula hirundo. 
t See Brug., Encyc. Method., pi. 189. 
X Improperly styled by Poli the abdominal trachea. 
