ACKPIIALA TKSTACEA. 85 



O. folium, h.; lb., Ixxi, 662, tJb'6. 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 Gorgqnific 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 sumaiit of the most convex valve greatly 

 projects and curves more or less into a hook, or is partially spiraf; 

 the other valve is frequently concave. The greater number of these 

 shells appear to have been free ; some of them, liowever, seem to have 

 adhered to ether bodies by their liookf. 



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, arc easily distin- 

 guished by their inequivalve semi-circular shell, almost always regu- 

 larly marked with ribs, V\'hich 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 | placed on a cylindrical jjedicle be- 

 fore a sac-like abdomen that hangs between the branchite. Some 

 species, known by a deep eaiargination under their anterior ear, are 

 furnished with a byssus. The others cannot adhere, and even swim 

 with rapidity by suddenly closing their valves. I'he mantle is sur- 

 rounded with two ranges of filaments, several of the external ones 

 being terminated by a little greenish globule. The mouth has ini- 

 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 are broad and longitudmally striated. The 

 animal is eaten. 



We may also remark the Sole of the Indian Ocean, Oslrea 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.fomicata; — O. 

 sinensis; — O. Forskahlii; — O. rostrata ; — O. virginica ; — O. cornucopice; — O. senega. 

 Icnsis; — 0. steUata; — O, ovalis ; — O.papyracca, and the Mytilus crista-galli ; — M. 

 hyotis; — .V. /rons, Gmel., and those figured by Brugi^re in the Encye. Method., 

 pi. 179, 188. 



It is almost certain, however, that several of these pretended species are mere 

 va.ieties. 



The Ost. semi-aurita, Gualt., 84, H, is a young Acicula hirumlo. 



t See Brug., Encyc. Method., pi. 189. 



X Improperly styled by Poll the abdominal Iracheu. 



