264 PNEUMONOBRANCHIATA. 



Dr. Turton's figure of Planorbis planatus certainly 

 represents this shell, and probably he only described 

 a young specimen. 



Draparnaud and Michaud believe that the Helix 

 contortuplicata Gmelin, S. Nat. n. 144. (Planorbe en 

 vis Geoff. 99. t. 3. f. 17, 18.) is only a monstrosity. 



Mr. Sheppard describes a monstrosity which had 

 the volutions nearly disjointed or pulledout. (Linn. 

 Trans, xvi. 157.) 



Mr. Alder observes, " I am not very sure, even 

 after the examination of Mr. Jeffreys' specimen, that 

 I perfectly understand the distinction between Pla- 

 norbis disciformis and P. carinatus. The degree of 

 carination is so very variable in different individuals 

 of the same species, that it is rather fallacious as a 

 distinguishing character." On re-examining the spe- 

 cimen here referred to, I could not find any character 

 of importance to distinguish them ; and Mr. Jeffreys 

 says, "they are often found living mixed with P. 

 carinatus" 



In the first edition of this work there was some 

 mistake about the reference to the figures, perhaps 

 occasioned by their being wrongly numbered by the 

 engraver. 



Planobis marginatus should have been 87, and 



not 88. 

 Planorbis complanatus should have been 88, and 



not 89. 



Planorbis carinatus should have been 89, and not 87. 



This is proved by the size he gives for Planorbis 



complanatus. Rossmasler has partly corrected this 



error ; he truly considers the P. complanatus of Turton, 



as only a state of growth of P. marginatus. 



