HELIX. 195 



shaped like a horseshoe. The teeth within the aperture 

 might escape notice if not looked for. The columellar 

 tooth varies considerably, being in some thin and oblique, 

 connected bj delicate lines of callus at either extremity 

 with the lip, in others larger and more prominent, with 

 the space between the two lines of callus more or less 

 filled up with testaceous matter. 



There is a variety with the upper surface flat, the strine 

 of increase very prominent and sharp, and more widely 

 separated, six entire whorls, acutely carinated, the base 

 exhibiting one and a half volutions and a deep umbilicus. 

 This, by some, would be considered a distinct species ; 

 but it does not seem to me to be entitled to any other 

 rank than that of a marked variety. 



This species was first described by Mr. Say, as Poly- 

 gyra plicata. A variety, differing in some slight parti- 

 culars, but found at a point very remote from the first, 

 was described by him as Polygyra fatigiata. Recently, 

 Mr. Lea has enlarged its synonymy by the addition of 

 two new specific names. The distinctions on which the 

 latter has founded his species, in this instance, are not, 

 I think, sufficient for that purpose ; if admitted to be 

 valid, they would lead to an infinite multiplication of spe- 

 cies, and burden the descriptive part of Natural History 

 with a mass of matter beyond the compass of any mind. 



Having in my possession original specimens of Poly- 

 gyra plicata labelled by Mr. Say, and having, through 

 the politeness of Mr. Lea, had the opportunity of examin- 

 ing the specimens from which he made his descriptions 



