AMERICAN SPECIES OF VERTIGO. 113 



loc.; Onion Valley, Kearsarge Pass, Inyo Co., J. H. Ferriss 

 and E. Hand, 1916. 



V. dalliana is a more conic, thinner shell, of different color, 

 having more rapidly increasing, more convex whorls, and a 

 larger aperture. Moreover, adult specimens of V. sterkii are 

 always toothed. V. andrusiana is generally larger, and so 

 far as seen, it always has much larger teeth. V. tridentata is 

 a far paler, more slender shell, with smaller aperture, stronger 

 teeth and a distinct auricle. 



In both of the localities V. sterkii occurred associated with 

 V. modesta castanea a form also characterized by degenera- 

 tion of the teeth. 



Group of V. coloradensis. 



Subcylindric, distinctly striate forms, the striation strong- 

 est on the penult whorl, related to the modesta and to the 

 ventricosa and gouldii groups. Typically they are mountain 

 snails 6000 ft. up ; but V. hannai and V. arthuri are from 

 the lower plains eastward. 



Key to species. 



1. 2 to 2.3 mm. long ; a low crest ; parietal and columellar 

 lamellae, sometimes an angular; 2 long palatal folds. 

 Alpine in Colo., N. M., Ariz. V. concinnula, no. 23. 

 1.5 to 1.8 mm. long. 2. 



2. No angular lamella. 3. 

 An angular lamella present ; crest wanting or very weak. 5. 



3. No noticeable palatal callus; a low crest. 1.7-1.9 mm. long. 

 Mountain forms. 4. 

 A strong palatal callus ; 1-1-3 teeth ; 1.5 x 0.8 mm. Western 

 Dakota. V. arthuri, no. 24. 



4. Teeth 1-1-2, no basal fold. V. coloradensis, no. 22. 

 Teeth 1-1-3, a basal present. V. c. basidens, no. 22a. 



5. Teeth 2-1-2, no basal fold. V. c. arizonensis, no. 22&. 

 Teeth 2-1-3, a basal present. 6. 



6. Diameter 1 mm. or more; striation irregular. Western 

 Kansas. V. hannai, no. 21. 

 Diam. under 1 mm. Santa Catalina Mts., Arizona. 



V. c. inserta, no. 22c. 



