PLANORBIS. 63 



being found abundantly in a number of localities in 

 almost every district, in ponds or ditches of stagnant 

 water, or slowly-running streams and rivers. 



P. VORTEX. Linnceus, PL VII, fig. 30. 



Shell depressed, thin, nearly flat above, concave beneath ; whorls 

 six or seven, convex above, flat beneath ; circumference somewhat 

 carinated. 



Helix vortex, Linn. 



Shell extremely depressed, discoid, about three 

 eighths of an inch in diameter, thin, transparent, and 

 closely wrinkled, of an olivaceous horn colour. The 

 body is broader above than below. Aperture a little 

 angular, broader than long. Volutions slightly con- 

 cave above, fiat underneath, which forms a sharp keel 

 at the base of the periphery. The animal varies in 

 colour, but is generally grey, with darker head. Ten- 

 tacles long. 



Hah. Widely distributed and common in most dis- 

 tricts, in ponds, ditches, and canals, preferring those 

 which flow slowly or are quite stagnant. 



P. spiRORBis. Linnceus. PL VII, fig. 29. 



Shell thin, depressed, concave both above and below ; mouth 

 roundish. 



Helix spirobis, Mont., Sfc. 



Very closely resembling the last species, but may be 

 distinguished by having both disks concave ; it is also 

 less, but rather thicker. The body consists of five or 

 six whorls, the outer one of which is not much carinated. 



Hah. Very much the same localities and situations 

 as the former ; they are very often found in the same 

 pond, though seldom so plentifully. 



P. coNTORTus. LmncBus. PL VII, fig. 31. 



Shell nearly flat above, deeply umbilicate beneath ; whorls closely 

 coiled but separated by a deep surture ; aperture narrow and crescent- 

 shaped. 



Helix contorta, Linn., 8^c. 



