ACEPHALA TKSTACEA. 85 



O. folium, 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 Gorgonire and other 

 Lithophytes*. 



M. de Lamarck separates by the name of- 

 GBYPH.EA, Lam., 



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

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

 projn-ts and curves more or less into a hook, or is partially spiral; 

 tin- other valve is frequently concave. The greater number of these 

 .shells apjM'ar 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 inequivalvc 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, 

 Poli, 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 eaiargination 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 : tn this genus are referred the Ost. orbicularis ; O. fornicata ; O. 

 rinensis; O. Forskahlii; O. rostrata ; O. virginica / 0. cornucopia; O. senega - 

 lensis; O. stellata; O. oralis ; O.papyracea, and the Mytilus crista-galli ; .!/. 

 hyolis; M.frons, Gmel., and those figured by Brugtere in the Encyc. Method., 

 pi. 17!), 188. 



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

 varieties. 



The Ost. semi-auritu. ' H. i* a young Acicula hi, undo. 



Brug., Encyc. Method., pi. 189. 



J I mproperly styled by Poli the abdominal trachea. 



