ACEPHALA TEStACEA. 395 



Gryph-ea, Lam., 



Certain oysters, mostly fossil, of the ancient calcareous and schist- 

 ous strata, in which the summit of the most convex valve greatly 

 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 hook(l). 



G. tricarinata. The only living species known. 



Pecten, Brug., 



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 always 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(2) placed on a cylindrical pedicle be- 

 fore a sac-like abdomen that hangs between the branchiae. 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 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 four- 

 teen ribs each, that are 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 

 valves, one brown, the other white, and internal ribs, fine as 

 hairs, approximated two by two(3). 



(1) See Brug., Encyc. Method., pi. 189. 



(2) Improperly styled by Poli the abdominal trachea. 



(3) Add the ninety-one species of Ostrea, Gmel.; \vc must remember, however, 

 that some of them are far from established on a solid foundation. For the fossil 

 species, consult Sowerby (Mineral Concholog-y), and Brong'niart, App. CUv., Oss. 

 Foss. tome II, Env. de Paris. 



