24 



scending to the aperture and deeply constricted 

 behind the peristome; above with rather regular, 

 low rib-striie, below rather finely and irregularly 

 striated. (Subg. Polygyra.) dorfeuilliana, Lea. 



— parietal tooth rather long, not complex; spire con- 



vex; surface usually hirsute (Subg. Stenotrema.) 3 



3 a notch in the basal part of the peristome; umbili- 



cus closed. 4 



— no notch in the white lipped peristome; umbilicus 



partly or entirely covered. monodon, Rackett. 



AW^'. — The type (monodon) has a diam. of from 10 to 12 mill, or 

 more, and the umbilicus is rather wide; var. fraterna (Say) is smaller, 

 its umbilicus narrow, almost covered by the reflected peristome; var. 

 Icaii (Ward) is still smaller (ab. to 7 mill, diam.) more conve.x, with open 

 umbilicus, and dark, shining surface; by some conchologists, the latter 

 is regarded as a species. 



4 diam. 10, alt. 6 mill., color reddish, stenotrema, Fer. 



— diam. 7, alt. 4 mill.; color brown; hirsuta. Say. 



Note: — the last two sp. are closely related, and considerably vari- 

 able. "In stenotrema the notch in the lip is is invariably small and more 

 central than in hirsuta." 



5 peristome asgular, with a strong lip, usually with 



teeth; always a strong, elongated tooth on the 

 parietal wall (Subg. Triodopsis) 6 



— peristome rather rounded, (rarely) somewhat angular, 



without teeth, except in some sp. a tubercular one 

 near the columella, then the aperture nearly circu- 

 lar; sometimes a tooth on the parietal wall (Subg. 

 MesocJon.) 11 



6 umbilicus covered. 7 



— umbilicus open. 10 



7 diam. 12, alt. 6.5 mill.; surface hirsute, color brown- 



ish to whitish; aperture very much contracted; 

 lip with two teeth directed inward. inflecta. Say. 



— diam. 18 to 25 mill. 8 



8 peristome usually not with well formed teeth; sur- 



face not hirsute, striated, sh. pellucid, reddish horn 

 colored; diam. 18, alt. 8 mill, appressa, Say. 



