70 PLANORBIS. 



often to be found on hedge-banks or chalk soils. 

 It is a pretty shell, sometimes white, often tinted 

 with purple. 



" In the family Lymmiana^ the species are 

 amphibious ; inhabiting fresh-water ; but rising 

 to the surface to breathe the air. They have 

 but two tentacula. 



" As several species are British, you may have 

 the satisfaction of examining them for yourselves. 



" The genera are, 



Planorhis Helix. 



Physa Bulla. 



Lymncea Helix. 



" Planorhis is a discoid shell, and one peculi- 

 arity of the genus is, that they are all reverse 

 shells. In a discoid shell the spire is depressed; 

 when held up, the whorls turn from right to left, 

 and the aperture is left-handed. The largest spe- 

 cies is P. cornu-arietis* which is a native of Bra- 

 zil. P. come us is common in ponds and ditches. 

 Empty shells are to be found at the edge of the 

 water. (Plate 9.) If you take the animal to ex- 

 amine, and study its habits, remember that you 

 have no right to injure it, and that you have al- 

 ready promised me that no kind of cruelty shall 

 take place. 



* Ram's-horn. 



