26 PLANORBIS DEFLECTUS. 



inner whirls, and, with the sutures, moderately 

 and equally excavated: last fourth of the ulti- 

 mate volution with a strong tendency to diverge 

 toward the left, (figs. 4, 5,) frequently not in con- 

 tact with the preceding whirl: aperture large, 

 very oblique: peritreme circular, except where 

 the labium advances upon the penult whirl. 



Color light corneous. 



Geographical Distribution. New England, 

 Ohio, Northwest Territory. 



OBSERVATIONS. 



The peculiar deflection of the aperture, in 

 most individuals of this species, and the want 

 of a sharp carina, readily distinguishes it from 

 P. exacutus. Unless the deflection be very 

 great, as in figure 5, the lower side can scarcely 

 be styled umbilicated, approaching P. parvus in 

 this respect. 



The species of this genus which have the 

 apex of the shell above, or on the right side, 

 appear to be most liable to deviations or mon- 

 strosities, and the whirls appear to vacillate in 

 their revolution, as if a certain maintaining 

 power were wanting, to impress, in a decided 

 manner, the same characters upon all the indi- 

 viduals of a species. 



