Our British Snails 55 



Planorhis (Gyrorbis) carinatus. — Larger than 

 spirorhis and vertex. Sharply keeled in the 

 centre of the,^ outer margin. Mouth angulated 

 above and below. Local, mainly in the south 

 and east of England. 



Planorhis {Gyrorbis) umbilicatus. — Like the last, 

 but the keel is below and not on the centre. 

 Mouth rhomboidal. More common than cari- 

 natus. 



Planorhis (Coretus) corneus. — Far the largest 

 species. Dark brown, lighter below. Mouth 

 nearly circular. Spire sunk. In boiling water 

 often exudes a crimson fluid. Common. 



Planorhis [Bathyomphalus) contortus. — Small, 8- 

 whorled, flat above, very convex below. Fairly 

 common in stih water. Very compact in appear- 

 ance. 



The sub-family Physa has two genera, Aplecta 

 and Phj^sa. 



Physa [Aplecta) hypnonmi is a spindle-shaped, 

 very glossy, semi-transparent, dark reddish brown, 

 shell, with 6 to 7 whorls. Not common. Found 

 in still water. 



Physa {Physa) fontinalis.— More common, and 

 found in running as well as in still water. Shorter 

 and more rounded than the last. Shell very 

 thin, greenish horn-colour. Lobes of the mantle 

 expand over the shell. Seen in an aquarium 

 are its perpendicular threads of mucus, up and 

 down which the animals climb. 



