PHYSA. 59 



an inch in length, the breadth being nearly one-fourth. 

 Animal lighter or darker grey, with long slender tenta- 

 cles of a paler colour. 



car. ACUTA is larger and narrower, with a more elon- 

 gated spire. This variety is by no means common. 

 The variety 2 of Gray has the last whorl rather angu- 

 lar behind, it is smaller than the normal form, and 

 recorded as being found " in very small plashes of 

 water or in water among grass." The difference 

 of situation is probably sufficient to account for the 

 variations. 



Hah. Streams, pools, &c., on aquatic plants in all 

 parts of the British Isles. 



P. HYPNORUM. Linnceiis. PL VII, fig. 26. 



Shell oblong, conical ; spire elongated and acute ; aperture oval 

 lanceolate. 



Bulla hypnorum, Mont. Aplexus hypnorum, Gray. 



This shell is in many respects similar to the preced- 

 ing, but differs from it in having a more elongated 

 spire, the last volution of which is not so ventricpse. 

 The whorls are depressed, glossy, and transparent. 

 Aperture lanceolate ovate. About half-an-inch in 

 length, and one-fifth of an inch in breadth. Animal 

 nearly black, foot long and lanceolate. 



Hah. Ditches, ponds, and slow running streams 

 throughout the British Isles, except the extreme north 

 of Scotland. It is as common, though somewhat more 

 local than the preceding. 



Planorbis. Muller. 



8hell — Spiral, discoid, dextral ; aperture lunate, margin en- 

 tire ; peristome simple, neither tliiclcened nor rcjlexed. 



Animal — A hroad head with two tentacles, having eyes at 

 their inner bases ; foot small. 



P. coKNEUs. LinncBUS. PL VII, fig. IT. 



Shell large, nearly flat above, deeply umbiiicate beneath ; whorls 

 five, wrinkled, deeplj- divided, convex above, flattened beneath ; aper- 

 ture semicircular. 



