, PLANOEBIS. 
239 
caused the keel to be considered as central^ which it 
is not. 
Dr. Turton’s figure of Planorhis 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. {Planorhe en 
visy Geoff. 99. t. 3. f. 17 y 18.) is only a monstrosity. 
Mr. Sheppard describes a monstrosity which had 
the volutions nearly disjointed or pulled out. {Linn. 
Trans, xvi. 157.) 
Mr. Alder observes : I am not very sure, even 
after the examination of Mr. J effreys’ 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 reexamining the spe- 
cimen here referred to, I could not find any character 
of importance to distinguish them ; and Mr. J effreys 
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. 
Planorhis marginatus should have been 87. and 
not 88. 
Planorhis complanatus should have been 88. and 
not 89. 
Planorhis carinatus should have been 89. and 
not 87. 
