PUPA. 335 



line semi-circular, the curve consisting of segments of two 



' *J ^J 



different sized, but well defined circles, the smaller on 

 the right at the junction of the lip and body whorl, com- 

 prising about one-fourth of the whole contour, and form- 

 ing an angle at their junction. Teeth six, two on the 

 transverse margin, two on the colurnellar margin, the 

 upper of which is massive, the lower pointed, and two on 

 the outer lip, in the base and at the junction of the two 

 curves, sharp and prominent; umbilicus expanded. 



Length three-fortieths of an inch ; transverse diameter 

 one-twenty-fifth of an inch. 



GEOGRAPHICAL DISTRIBUTION. Inhabits all the 

 Northern, Middle, and Western States. Is common in 

 Massachusetts. 



KEMARKS. Of forty specimens of this shell examined 

 by me, with the aid of a microscope, one had a single 

 tooth, two had three teeth, and twenty-eight had two 

 teeth, upon the transverse margin, the one nearest the 

 centre being always largest and most prominent ; and all 

 of them had the bilobate, or double curved aperture, and 

 the irregular indentation upon the outer whorl, near the 

 lip. A single specimen had three teeth upon the lip, 

 and three upon the transverse margin, making, with two 

 upon the columellar margin, eight in all. The semi-cir- 

 cular mouth is abruptly truncated by the last whorl, which 

 forms a distinct and nearly transverse limit. The lip is 

 thin and a little turned outwards, its edge is often whit- 



