LYMN^A. MELANOPSIS. VALVATA. 71 



" P. vortex is a smaller species. The outer 

 valve is carinated. 



" Physa is found in fresh-water upon aquatic 

 plants. They are small shells. 



" The animal of the LymncBa genus has two 

 flat tentacula. L. stagnalis is a very pretty 

 spiral shell, common in ponds. 



" L. auricularia is also frequent. It is much 

 smaller than the first species. The last whorl is 

 swelling, and the aperture very wide. They 

 are both thin and brittle. 



*' The family Melaniana are chiefly foreign. 

 The shells are covered with a dark-coloured epi- 

 dermis. They are operculated. 



Melania Helix, 



Melanopsis. 



" A species of Melanopsis inhabits the river 

 Orontes, in Syria. 



" There is yet another family connected with 

 Helix, the Peristomata, containing 



t^alvata. 



Paludina Helix* 



Ampullar ia Helix, par tly . 



" Some of the Valvata genus are found in fresh- 



