limn^ead^:. 263 



Helix planorbis. Linn. S. Nat. i. 1242.; Turton, 



Diet. p. 45. 

 Helix complanata. Mont. T. B. 450. t. 25. f. 4. 

 Planorbis complanatus ? Turton, Man. ed. 1 . f. 



89. (not description). 

 Var. 1. Planorbis disciformis. Jeffrey s^ Linn. 



Trans, xvi. 521. ; Alder, Mag. Z. 8f B. ii. 113. 

 Planorbis lutescens. Jeffreys, Linn. Trans, xvi. 



385. (not Lam.). 

 Helix carinata. Mont. T. B. 451. t. 25. f. 1. 

 Planorbis planatus. Turton, Man. ed. 1. 110. 



f. 92. 



In stagnant waters. 



Animal brown. 



The animal, according to Montagu, differs from 

 P. marginatus in the tentacles being somewhat longer, 

 and particularly in their being pellucid, yellow, and 

 not darker in the middle. (T. B. 453. ; Sturm, 1 43.) 



Shell hardly half an inch in diameter, with five 

 volutions, the outer one growing suddenly larger, 

 above nearly flat, beneath rather convex, gradually 

 shelving to the outer edge ; in the older specimens, 

 the hinder or upper part of the whorls becomes rather 

 convex; colour pale horn-colour and transparent, 

 often covered with a brownish coat; aperture con- 

 tracted to a point above, in consequence of the keel. 



This species is immediately known from Planorbis 

 carinatus by the under or front side of the whorls not 

 being so convex and ventricose, by their shelving gra- 

 dually to the outer edge, and by the hinder or upper 

 part of the whorls of the older shells being rather 

 convex, somewhat like the lower, which has caused 

 the keel to be considered as central, which it is not. 



