OP CONCHOLOGY. 55 



outer lip, a somewhat larger tubercle, and inflected, lip covering 

 the umbilicus. Light horn color. 



Diam. 11, height 4-5 mill. 



Western Pennsylvania to Michigan, and southwards to Texas. 



The constriction of the whorl behind the aperture is so great 

 in this species that the reflected lip does not project beyond the 

 general circumference of the shell. 



2. Isognomostoma Rugeli, Shuttleworth. 



Plate 9, figure 8. 



Shell convex, depressed, rather smooth ; spire convex, but 

 little elevated, suture well marked ; whorls 5|, narrow, closely 

 revolving, the last very much contracted in the centre behind 

 the lip ; aperture small, with a prominent bent, oblique parietal, 

 lamellar tooth, a small upright tubercular basal tooth, and a 

 large lamellar tooth opposite to the parietal tooth, and situated 

 entirely farther within the aperture ; base convex, umbilicus 

 covered. Light horn color. 



Diam. 10—13, height 5—6, mill. 



Tennessee and North Carolina. 



Easily distinguished from I. injiecta by its upper lip tooth, 

 situated far within the aperture. 



STENOTREMA, Rafinesque. 



In this genus the shell is orbicular and generally hirsute, the 

 whorls revolve closely, and the aperture is basal and narrowly 

 transverse, extending from the periphery to the axis. In most 

 of the species the dentition of the aperture in Stenotrema is 

 peculiar to this genus — namely, a long transverse parietal blade 

 and a parallel thickening of the basal portion of the lip, which 

 is frequently incised in the middle. 



Stenotrema inhabits the entire extent of the United States, 

 and several of its species are widely difl'used, wliilst others, on 

 the contrary, are extremely local, and two or three of them very 

 rare and highly esteemed. 



