110 



92. PLANORBIS planatus. Shell whitish, striolate, a 

 little concave on both sides, the outer volution with 

 a sharp carinated edge in the middle. 



Helix carinata. Mont. p. 451. t. 25. f. 1. 

 Plancrbis spirorbis. Drap. p. 45. t. 2. /. 8, 9, 10. 

 , , Leach, Mollusc, p. 153. 



Shell not a quarter of an inch in diameter, pale horn- 

 colour when fresh, but generally found of a dull 

 opake white, with four or five volutions, which 

 gradually sink at the centre on both sides, but 

 rather more beneath ; the outer one proportionately 

 larger, a little convex and equally sloping on both 

 sides to a sharp but not prominent edge : aperture 

 heart-shaped, acute at the top. 



This is a rare shell, and has not been well understood. 

 Montagu has properly described it, observing that 

 the outer volution slopes gradually to a sharp 

 carinated edge. The H. Spirorlis of Linne it cannot 

 be, for he remarks that it has not the least ap- 

 pearance of keel, " anfractibus quinque teretibus," 

 and again " minime marginatis." 



In slow streams, but rarely. 



93. PLANORBIS fontanus. Shell dark horn-colour, 

 smooth, glossy, very convex above, flat and um- 



