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those which are of an elongated form, and have a groove or line running 

 along the disk of the valve, from which the folds part on each side, like 

 the teeth of a comb. 



Under the first of these sub-divisions may he placed O. diluviana, Linri. 

 which is a shell as large, and even larger, than the common oyster, 

 being plicated, and having the margin formed by acute-angled teeth, 

 like those of a saw, and placed at right angles with the surface of the 

 shell : the margin being finely striated by the apposition of the different 

 lamellse. A small specimen of this species is represented Plate XV. 

 Fig. 1 . Shells very nearly, if not exactly, agreeing with these fossils, 

 have lately been found in the South Sea. O. crista galli, the fossil cocks- 

 comb oyster, appears to be of this same species. O. flabdlula, Lam. is 

 oblong, cuneiform, slightly bent, with long rough plicae : the upper valves 

 flat. This shell much resembles Chama plicata altera, Brand, and there 

 also exists a considerable agreement in the hinge ; for, on a superficial 

 view, the hinge of this shell would be supposed to be that of a Chama : 

 the cartilage pit is very oblique and deeply sunk, giving much of the 

 appearance of the receptacle of the oblique tooth of the Chama. 



The shells of the second subdivision have very much the appearance of 

 a leaf. Such is the fossil oyster from France, Plate XV. Fig. 4, in which 

 the shell, although now perfect stone, retains its original surface and 

 shelly lustre. This species, O.frons vd folium is known to the continental 

 oryctologists as Lafeuille de laurier. 



Plate XV. Fig. 2, is a beautiful and rare French fossil of this sub- 

 division, they being hardly ever found in so perfect a state. This shell 

 is also known as a Crete du Coque, or crista galli ; and it must, perhaps, 

 be admitted, that this appellation applies better to its form than to that 

 of any of the preceding shells. This specimen enables us to form a true 

 notion of the shape of the shell, which has not yet been correctly shown. 



VOL. in. p F 



