is very frequently found. Among the Hampshire fossils is a very curious 

 cardium, C. porutosum, Brand, on the longitudinal costae of which are 

 disposed thin, carinated, and crenulated plates, which are perforated at 

 their base. C. discors, C. porulosum, C. asperulum, C. calcitrapoides, C. ob- 

 liquum, C. granulosum, C. li?na, and C. heteroclitum, are given by La- 

 marck as the species found in the environs of Paris. 



CVI1. Crassatella. An equivalved inequilateral, close bivalve. The 

 hinge teeth, two, wjth an adjoining pit : the lateral teeth obsolete. The 

 cartilage inserted in a pit formed in the hinge. 



The genera Crassatdla, Lutraria, and Mactra, agree in having the car- 

 tilage of the valves interior, and attached to the hinge-pit of each valve ; 

 but this genus differs from the other two, in there being no gaping when 

 the valves are shut. 



C. tumida, Plate XIII. Fig. 2, much resembles a recent species of this 

 genus, which was found at King's Island, in the South Seas, by M. Pe- 

 rpn. The shells of this, as well as of some other species of this genus, 

 acquire a considerable degree of thickness with age. One specimen 

 which I possess, from Grignon, which is about three times the size of 

 that which is here delineated, weighs nearly half a pound. C lamellosa, 

 Lam. has been supposed to be the same shell which is figured by Bran- 

 der, among the Hampshire fossils, as Tdlina sulcata, Fig. 89 ; but the 

 English shell differs, in its form, from the French one, according to the 

 specimens in my possession: the English one terminating, at its anterior 

 side, in a more determinately pointed rostrum than the French one does. 

 This, however, may be only the difference of a variety. C. compressa, 

 Lam. resembles the species just mentioned, except in being less elon- 

 gated transversely, and in its ridges being much smaller and closer. 

 Four more species, C. sulcata, C. gibbosula, C. l&vigata, and C. triangularis, 

 are found in the neighbourhood of Paris 



CVIII. Paphia. A subtransverse inequilateral shell, with close valves, 

 and having the cartilage internal. The pit for its insertion is under the 

 beaks, between or beside the teeth of the hinge. 



