NOTE. 



Not having had the advantage of examining M. De- 

 shayes s admirable work on the fossil shells of the Paris 

 basin, until after a part of the foregoing descriptions were 

 printed off, it has, necessarily, been out of my power to 

 make any comparisons with his species. The following 

 seem important enough to be introduced here. 



Pasithea umbilicata (nobis), page 103, resembles M. De- 

 shayes s figure (Coquilles Fossiles, pi. 9, figs. 1 and 2,) 

 of Lamarck s Bulimus terebellatus. 



All the species figured by M. Deshayes as Melanm, in 

 pi. 13, vol. 2d., and part of those of pi. 14, belong to the 

 genus Pasithea (nobis). It must be evident, to every geolo 

 gist, that the division of fresh water and marine shells, is all 

 important, involving facts of the highest interest, as re 

 gards alternate strata, such as exist in the Paris basin. 

 If we do not make the breathing of salt and fresh water a 

 sufficient character, as well as that of breathing air, for 

 generic distinction, we cut ourselves off from the use of a 

 most valuable characteristic, to designate the strata of 

 groups, see p. 99. 



Venericardia rotundata (nobis), resembles V. squamosa, 

 of Lamarck, as figured by M. Deshayes, pi. 26, figs. 9 

 and 11. 



