26 



1 7 without a parietal tooth (usually); last whorl and 



aperture somewhat flattened below; aperture form- 

 ing a smaller angle with the plane of the base; lip 

 broad; diam. 30, alt. 17 mill. . albolabris, Say. 



— with a oarietal tooth (sometimes wanting) ; last 



whorl and aperture more rounded, the latter less 

 indined; diam. 28, alt. 17 mill. exoleta, Binn. 



N'ote: — There are decided differences in anatomy between the last 

 two sp. 



18 umbilicus narrow and partly covered by the re- 



flected peristome; peristome without a tooth. 19 



— umbilicus rather wide; peristome with tooth near 



the columella; sh. large, depressed. 20 



19 umbilicus quite narrow; no parietal tooth, sh. rather 



globose, yellowish horn colored; diam. 18.5, alt. 

 II. 5 mill. clausa, Say. 



— umbilicus moderate; a small parietal tooth; sh. 



slightly depressed, horn to reddish horn colored; 

 diam. 22, alt. 13 mill. thyroid.es, Say. 



20 no parietal tooth; sh. yellowish horn with brown re- 



volving bands (sometimes wanting); aperture al- 

 most circular; diam. 28, alt. 14 mill. profunda, Say. 



— with parietal tooth; aperture lunately subcircular; 



color light russett, surface shining; diam. 27, alt. 



17 mill. sayi, Binn. 



16. Strobilops. Pilsbry. 



I Spire depressed conic; last whorl more or less dis- 

 tinctly carinated-angular, internal lamella^ on outer 

 wall 3 to 4; color deep horn to chestnut. 



labyrinthicus, Say. 



— spire rather high, dome-shaped, last whorl rather 



well rounded at the peripher}'; lamellae inside the 

 outer wall 5 tQ 7? in a spiral line; color, horn to 

 grayish. virgo, Pils. 



