56 AMERICAN JOURNAL 



* Umbilicus open, or partly covered. 

 1. Stenotrema monodon, Rackett. 



Plate 9, figures 18, 20. 



Shell convex, depressed ; spire slightly elevated, suture very 

 distinct ; whorls 5, convex, narrow, finely striated and minutely 

 hirsute, or covered with the scars of the hairs, deeply grooved 

 behind the reflected lip ; aperture transverse, with a long oblique 

 parietal tooth, outer lip narrowly reflected, its basal termination 

 more or less encroaching on the umbilicus ; under surface very 

 convex, much impressed around the deep, narrow, more or less 

 closed axis. Dark horn color. 



Diam. 7—10, height ^—^ mill. 



Inhabits the whole country east of the Rocky Mountains. 



This is a somewhat variable species, and varieties of it have 

 been considered distinct by several American conchologists. 

 The typical monodon is supposed to be restricted to those species 

 of large growth and open umbilicus, while fraterna, of Say, is 

 the name applied to those having the umbilicus covered. A 

 more convex variety, with narrower whorls, and generally smaller 

 size, is called H. Leaii, Ward. We are told that the latter 

 afiects moist situations, while the true monodon inhabits dry 

 places. I agree with Messrs. Binney and Bland in believing 

 that we have not yet sufficient data to justify the separation into 

 species of these varieties of monodon. 



** Umbilicus closed. 



t Periphery rounded. 



X Outer lip incised in the middle. 



2. Stenotrema stenotrema, Ferussac. 



Plate 9, figures 21, 30. 



Shell subglobose, depressed ; spire convex, somewhat conical, 

 suture well impressed ; whorls 5, well rounded, narrow, slowly 

 increasing in size, subangulate on the periphery, more convex 

 below, and slightly impressed in the umbilical region, finely 

 striate, and covered with close short hairs ; aperture very narrow, 

 extending to the axis of the shell below, and almost closed by 

 the long lamelliform, outwardly projecting parietal tooth, the 

 narrow depressed outer lip is reflected close upon the whorl, with 

 a small triangular notch in its centre. Chestnut brown, lips 

 white or pink. 



Diam. 10, height 6 mill. 



Western and Southern States. 



