﻿PROSOBRANCHIATA. 



337 



used by the late Mr. Alder for a variety of Succinea putris (very well figured by Capt. 

 Brown in his ' Brit. Conchology/ pi. xlii, figs. 34, 35), and I thought the double use of 

 this name would cause confusion. Our present shell so much resembles a species 

 figured and described by M. Deshayes that I have referred it as probably identical, 

 though with doubt, as I am unable to compare it with a specimen of the French Eocene 

 species and have to rely on the figure. In describing this fossil M. Deshayes observes 

 that it is exceedingly difficult with his shell (of which I presume he must have had more 

 than one specimen, as he speaks of it as being in his own cabinet and also that of 

 M. Dutemple) to point out a difference. He says (p. 795), " Cette espece a beaucoup de 

 rapports avec le Succinea putris, qui habite en Europe ; mais elle n'en a pas moins avec 

 d'autres qui se plaisent dans les regions chaudes de l'lnde et de l'Amerique," and I can 

 fully endorse this remark. In comparing the figure of our shell with specimens of the 

 common living British species in my own cabinet (S. putris) there does appear to be a 

 slight difference, the fossil having its volution a trifle less inflated or convex, or rather 

 they seem to be more depressed. The French shell is from the " Lignites of Bernon near 

 Epernay," a deposit which is considered to be equivalent to our Lower Eocene, whereas 

 ours comes from the upper division of that formation. It is to be feared we attach 

 more importance to trifling variation in our specific determination of these freshwater 

 shells than we do to those which come from salt-water deposits. 



Genus 31^.— Bythinia. 1 Gray, 1824 (Prideaux, MS.). 



Generic Character. Shell conical, turbinated ; volutions convex ; aperture slightly 

 angular behind ; peristome simple, entire, continuous ; operculum testaceous, irregularly 

 concentric, with its nucleus nearly in the middle. 



Animal oviparous, eyes sessile. 



This genus has been separated from Paludina in consequence (as it is said) of its 

 being oviparous, while Paludina is ovoviviparous ; but this distinction is not well 

 established, and if it were it would be unavailing to the palaeontologist. It differs in 

 having a calcareous operculum, while in Paludina this is corneous. It is also said that 

 the eyes of Bythinia are somewhat differently placed. 



1 The name for this genus has been variously spelt : 

 Bithinia, J. E. Gray, G. P. Deshayes. 

 Bithynia, Watelet. 

 Bythinia, Jeffreys, Sandberger. 



