BYTHINIA. 25 
Genus I1.—BYTHINIA. 
1. B. renracuLAtTa (with tentacles). 
Somewhat conical, rather solid, glossy, semi-transparent, 
horn-coloured ; whorls six, convex ; sutwre moderately deep ; 
mouth oval, angulated above; wmbilicus 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. Leacuit (after Dr. Leach). 
Conical, rather thin, moderately glossy, semi-transparent, 
horn-colour ; whorls five, very convex; mouth almost cir- 
cular, with slight angulation above; wmbilicus small, but 
distinct; operculwn 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 :— 
