98 PHYTOPHAGA. 



In canals and ponds ; common to all parts of 

 England. 



Animal whitish ; trunk grey rugose. 

 Shell nearly a quarter of an inch long and as much 

 broad, globular, thin, light horn-colour, very finely 

 spiral-striate, and marked with some obscure concen- 

 tric lines ; spire of four volutions, tumid, and deeply 

 denned, and having much the appearance of a Trochus, 

 with a deep central umbilicus ; operculum dull grey- 

 ish white. 



Mr. Alder states that he received specimens of V, 

 depressa of PfeifFer, from Lancashire, 

 A JL some years ago, by Mr. Kenyon. 



They are exactly similar to those in 

 M. Ferussac's cabinet, received 

 from PfeifFer himself; but it can 

 scarcely, he observes, be considered more than a 

 variety of V, piscinalis. I think this opinion is fully 

 borne out by the examination of some specimens 

 which Mr. Kenyon has kindly sent to the British 

 Museum collection. Nilson and Forbes agree in this 

 opinion, and as the former justly observes, all conoid 

 shells are more depressed in their young state, from the 

 peculiarity of their formation. (See f. a. b. c.) 



The animal and operculum are well described by 

 Montagu (Test. Brit. 351.), who justly compared the 

 animal to that of the next species, though in his ar- 

 rangement one shell is a Turbo and the other a Helix ; 

 but he saw the difficulty of this arrangement. See his 

 note at p. 367., and also at p. 461., where he describes 

 the animal of V. cristata. 



8. 2. Valvata cristata. Crested Valve Shell, (t. 8. f. 



