182 



lutrarise, crassatellse, &c. ; but a generic difference, in the opinion of 

 Lamarck, exists in these shells : the cartilage is inserted in a pit between 

 the hinge-teeth. He believes that the shells of this genus are o-ilj found 

 fossil, and enumerates eleven species found in the environs of Paris: 

 E. l&vis, E. peliucida, E. trigonia, E. in&quilatera, E. fragiiis, E. elliptica, 

 E. imdulata, E. pellucida, E. obscura, E. miluiria^ and E. radio la fa. Plate 

 XIII. Fig. 13 and 14, are representations of the inner and outer sides of 

 E. l&vis, copied from Lamarck. 



CXIL Petricola. A tranverse inequilateral shell, gaping a little at 

 both ends, and having two muscular impressions: two hinge-teeth on 

 one valve, and a bifid one on the other. The cartilage external. 



Venus litkophaga, Linn, is given as a species of this genus, which has 

 not been described in a fossil state. 



CXIII. Donax. An equivalved inequilateral bivalve : the fore side 

 the bluntest. The hinge-teeth two, either in one or both valves : the 

 lateral teeth one or two, rather distant. 



The shells of this genus are strongly characterized by their nearly tri- 

 angular figure, derived chiefly from the obtuse, and, as it were, trun- 

 cated form of the fore side. When they have two lateral teeth, they 

 are situated one on each side, with the hinge-teeth between them. The 

 hinge-teeth themselves are sometimes two on each valve, and sometimes 

 there are two on one valve, and but one on the other. 



Lamarck describes the following species as having been found in the 

 neighbourhood of Paris : D. retusa, D. incompleta, D. tellinella, D. nitida, 

 D. lunulata, and D. obliqua. 



Plate XIII. Fig. 6, is a very small specimen of a fossil-shell which is 

 very frequently found in Gloucestershire and Somersetshire, near to Bath. 

 I have introduced it in this place, not knowing one more appropriate, and 

 trusting that its form may excuse a temporary disposal of it here, until 

 a more satisfactory examination may detect its real characters, which, 

 I think, will be found different from those of any known recent shell. 



