THE NAUTILUS. 53 



This small species is about the size and shape of an Amnicola 

 as suggested by the specific name. But, although the colu- 

 mella is scarcely at all calloused, the distinct thickening of the 

 outer lip and the projecting angle at the junction of the outer 

 lip and the colnmella forbid its reference to that genus. It is 

 entirely unlike any of the other species known from Arkansas 

 and quite different from any of the eastern forms. 



SOMATOGYRUS CRASSILABRIS n. Sp. Fig. 4. 



Shell subglobose, scarcely perforate, very thick and solid, 

 greenish horn-color, smooth with very fine lines of growth. 

 Spire short, subacute and small in comparison with the body- 

 whorl. Whorls 4. Apical whorl small, rounded, constricted 

 by a rather deep suture, everted, obliquely flattened above, 

 strongly and regularly spirally punctate above from the tip, 

 lirate below. The second and third whorls rather rapidly in- 

 crease in size, are rounded above, but less below, the suture 

 being well impressed. Body-whorl large, obtusely shouldered, 

 obliquely flattened above the shoulder, distinctly flattened be- 

 tween the shoulder and the periphery, below which it is rounded. 

 Aperture rather large, narrower, but scarcely angled above, and 

 obliquely rounded below. The outer lip is scarcely modified 

 by the shoulder, very thick and heavy, rounded and distinctly 

 everted below. Columella very thick and heavy, rounded. 

 Inner lip adnate to the parietal wall and heavily calloused. 

 The whole aperture is surrounded by an excessively thick de- 

 posit of callus. Umbilicus small, scarcely perforate, with a 

 distinct groove below. 



Alt. 4.33, diam. 4 mm. 



Types (No. 38823 Coll. Walker), from rocks on muddy bank 

 of the North Fork, Norfolk, Ark., collected by A. A. Hinkley. 

 Cotypes in his collection. 



This species, though evidently related to wheeleri by reason of 

 its shouldered body-whorl, differs decidedly in the characters of 

 the apical whorls, the less pronounced shouldering of the body- 

 whorl, the smaller umbilicus and, especially, in the remarkable 

 thickening of the aperture. In this particular it is quite distinct 

 from any of the other described species. 



