70 SUPPLEMENT TO THE CRAG MOLLUSCA. 
Hythe. This I have referred to Paludina contecta of Millet. ‘The volutions are very 
convex, with a deep sutural line, and the apex is very acute. 
PaLupINna vivipara, Liané. Supplement, Tab. I, fig. 5. 
Hex vivrpara, Linné. Syst. Nat., 12th ed., p. 1247. 
PALUDINA VIVIPARA, Forbes and Hanley. Vol. iii, p. 11, t. Ixxi, f. 14, 15. 
Localities. Chiilesford bed, Easton Bavent Cliff. Lower Glacial, Rackheath. 
The specimen figured is that of a small individual from Rackheath, but since it was 
engraved a full-grown specimen has been obtained by Mr. Cavell from Haston Cliff. 
All these fossil forms differ so materially from each other, that 1 have placed them 
under separate names. They have in all probability descended from a common ancestor, 
and most hkely P. /enta stood in that position, but altered circumstances materially . 
altered their forms, so as to make them permanent varieties, which it is difficult not to 
call species. 
I therefore refer my figured specimens in the following manner :— 
Paludina media. Crag Moll., vol. 1, Tab. XII, fig. 1. 
—  Clactonensis (P. diluviana, Kunth ?). Supplement, Tab. I, 
fig. 4, a, 6. 
—  glacialis. Supplement, Tab. IV, fig. 14, a, 6. 
—  vivipara. Supplement, Tab. I, fig. 5. 
—  contecta, mol, ° ANalo, IL, ie, OG 0. 
The species of the genus Pal/udina ave of difficult determination, and naturalists are 
far from being in accord respecting their specific limitations. M. Deshayes says ( Hist. 
des An. sans Vert.,’ vol. 1, p. 483): “ Nous devons affirmer n’avoir jamais vu une espéce 
vivante quelconque, absolument identique avec l’espéce fossil d’Angleterre ou de France ;” 
speaking of the Older Tertiaries. When I applied to Mr. Jeffreys for his opinion 
respecting the Clacton shell, he replied in letter, March, 1865, (with permission to quote 
his opinion), “I could find no difference between those (the Clactonensis) and crag 
specimens. I consider the P. /enta from the so-called upper Eocene Beds and your 
P. parilis or P. lenta of the Crag as the same species, and that this species (including 
each fossil form) is distinct from P. wnicolor of the Nile.” In the discussion on one of 
Myr. Prestwich’s papers upon the Crag (‘ Quart. Journ. Geol. Soc.,’ vol. xxvi, p. 282), 
Mr. Jeffreys, however, calls the Crag species Paludina unicolor ; from which it would 
seem that this opinion of 1865 has been modified. It must be admitted that the specific 
determination of the various forms of this genus is in an unsatisfactory state. 
