FRESHWATER AND LAND SHELLS. 107 



POLYGYRA DORFEUILLIANA. Plate XXIV. fig. 118. 



Testa supernh obtuso-conicd, infemh subinjlala, nitida, cornea, longitudinaliter striata, 

 lati umbilicata ; anfractibus senis; aperturd lunatcl, tridentatd. 



Shell above obtusely conical, below somewhat inflated, shining, horn-colour ; longi- 

 tudinally striate, widely umbilicate ; whorls six; aperture lunate, three-toothed. 



Hab. Ohio. Mr Dorfeuille, Cincinnati. 



My Cabinet. 

 Diam. -3, Length '2 of an inch. 



Remarks. — I adopt Mr Say's genus Polygyra. believing the divi- 

 sion, though very artificial, quite as good as many made by Lamarck. 

 This species has, like Polygyra fatigiai a (Say) and P. plicata (Say), 

 one large tooth on the left lip and two smaller ones on the right lip. 

 It differs from the first in not being carinate, from the last in being 

 larger and having larger striae. In the Dorfeuilliana the tooth on the 

 left lip is large and square, with an indentation in the centre. The 

 view into the mouth is nearly obstructed by the teeth, leaving, to ap- 

 pearance, three nearly square apertures. The superior part of the shell 

 is striate, while the inferior part is nearly smooth, and exhibits two 

 volutions. I have seen but a single specimen, which I believe is the 

 only one obtained by Mr Dorfeuille, who obligingly sent it to me. 



Polygyra Troostiana. Plate XXIV. fig. 119. 



Testa supernh subplanulata, infernh subinflatu, cornea, longitudinaliter striata, lath umbi- 

 licata ; anfractibus senis ; aperturd lunatd, tridentatd. 



Shell above nearly flat, below somewhat inflated, horn-coloured, longitudinally stri- 

 ate, widely umbilicate; whorls six; aperture lunate, ihree-toolhed. 



Hab. Tennessee. Professor Troost. 



My Cabinet. 



Cabinet of Professor Troost. 



Diam. -4, Length -2 of an inch. 



