70 SUPPLEMENT TO THE CRAG MOLLUSCA. 



Ilythe. This I have referred to Paludina conlecta of Millet. The volutions are very 

 convex, with a deep sutural line, and the apex is very acute. 



Paludina vivipara, Linne. Supplement, Tab. I, fig. 5. 



Helix vivipaka, Linne. Syst. Nat., 12th ed., p. 1247. 



Paludina vivipaiia, Forbes and Hartley. Vol. iii, p. 11, t. lxxi, f. 14, 15. 



Localities. Chillesford 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 Easton 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 likely P. lenta 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. i, Tab. XII, fig. 1. 



— Clactonensis {P . diluviana, Kunth?). Supplement, Tab. I, 



fig. 4, a, b. 

 — ■ glacialis. Supplement, Tab. IV, fig. 14, a, b. 



— vivipara. Supplement, Tab. I, fig. 5. 



— contecta, id. Tab. 1, fig- 6, a, b. 



The species of the genus Paludina are of difficult determination, and naturalists are 

 far from being in accord respecting their specific limitations. M. Deshayes says {' Hist, 

 des An. sans Vert.,' vol. ii, p. 483) : " Nous devons affirmer n'avoir jamais vu une espece 

 vivante quelconque, absolument identique avec l'espece 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. lenta 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. unicolor of the Nile." In the discussion on one of 

 Mr. 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. 



