PROSOBRANCHIATA. 337 
used by the late Mr. Alder for a variety of Swecinea putris (very well figured by Capt. 
Brown in his ‘ Brit. Conchology,’ pl. 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 espéce 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 I’Inde et de ’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 31st.—Bytuinta.’ 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 Pa/wdina is ovoviviparous; but this distinction is not well 
established, and if it were it would be unavailing to the paleontologist. It differs in 
having a calcareous operculum, while in Pa/udina 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. BE. Gray, G. P. Deshayes. 
Bithynia, Watelet. 
Bythinia, Jeffreys, Sandberger. 
