112 



d. with the vokitions detached and raised above 

 each other. 



Shell the tenth of an inch in diameter, of a blackish 

 or greenish horn-colour, with three volutions; 

 the epidermis raised into numerous transverse 

 ridges which form a spinous crest round the outer 

 margin : aperture roundish-oval, united all round, 

 and often detached from the second volution at its 

 narrower end. 



The variety d. is twice as large as others, and is re- 

 markable in having the volutions produced, de- 

 tached, and placed obliquely on each other. It 

 has been noticed both by Brard, p. 164. and by 

 GeofFroy. 



In ponds and ditches, on aquatic plants. 



•j-j" The outer volution rounded and without keel. 



95. Planorbis corneus. Shell deeply umbilicate 

 above, nearly flat underneath : aperture semicir- 

 cular. 



Planorbis corneus. Drap. p. 43. t. \.f. 42 — 44. 



Brard, p. 147. t. 6./. 1, 2. 



Sowcrhy, Genera, fg. 1. 



Helix cornea. Linn. Mont. Turton. 



