86 LIMN^IDiE. 



Norwich^ and measure nearly a quarter of an inch in 

 diameter. It is distributed throughout the greater part 

 of the Continent, and ranges from Sweden to Corsica 

 and Algeria. According to the Rev. R. T. Lowe, it also 

 inhabits Madeira. 



This species differs from P. albus in its smaller size 

 and glossy aspect ; in the upper side being rather convex, 

 instead of flat (owing to the rotundity of the whorls) ; 

 in its deeper suture and umbilicus ; in the upper part of 

 the outer lip not projecting so much, in consequence of 

 which the mouth appears to be more circular; and, 

 especially, in not having the strong and regular spiral 

 striae which characterize the last species. The mouth is 

 also not nearly so large; and the periphery is never keeled 

 or compressed. The present species is equally abundant 

 where it occurs ; but I am not aware that both species 

 have been found living together. 



It is the P. Icevis of Alder, and probably also the 

 P. cornu of Ehrenberg from the Nile. The P. Ross- 

 mcessleri of Auerswald appears to be only a large variety 

 of the same species, ha\'ing the peristome thickened by 

 an inner rib (as in the next species), judging from Ross- 

 massler's description and figure, as well as from an ex- 

 amination of typical specimens in the Museum at the 

 Jardin des Plantes. Von Martens has published, in the 

 ^ Malakozoologische Blatter^ for 1859, some excellent 

 dissertations on the synonymy of a few of the European 

 land and freshwater shells, and is of opinion that this 

 species is also the P. gyrorbis of v. Seckendorf and has 

 five other aliases. 



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