BYTHINIA. 25 



Genus II. BYTHNIA. 



1. B. TENTACULATA (with tentacles). 



Somewhat conical, rather solid, glossy, semi-transparent, 

 horn-coloured ; whorls six, convex ; suture moderately deep ; 

 mouth oval, angulated above ; umbilicus hardly perceptible ; 

 operculum thick. 



Found in slow rivers, canals, ponds, &c., dis- 

 tributed throughout every part of the British Isles. 

 Var. I. ventricosa. Shell white, tumid. 

 Var. II. decollata. Upper whorls wanting. 

 Var. III. excavata. More tumid, suture deeper. 



2. B. LEACHII (after Dr. Leach). 



Conical, rather thin, moderately glossy, semi-transparent, 

 horn-colour ; whorls five, very convex ; mouth almost cir- 

 cular, with slight angulation above ; umbilicus small, but 

 distinct ; operculum as in last species. 



This species is far more local and less abundant 

 than the last, though found in similar situations. It 

 occurs in Berks, Hants, &c. As it is only about half 

 the size of B. tentaculata, adult specimens cannot be 

 mistaken; but in case it should be mistaken for the 

 young of that species the following distinctions may 

 be useful: 



