76 AMERICAN SPECIES OP VERTIGO. 



& 2 . Without the above combination. 



c 1 . 6-9 teeth; crest or auricle generally well de- 

 veloped ; rather strong, dark colored forms 

 (pi. 6). Group of V. ovata, species nos. 1-6. 

 c 2 . 2-6 teeth (pi. 7). 



Group of V. pygmcra, species nos. 8-20. 

 c 3 . 4-6 teeth; shell cylindric or oblong, striate. 



Group of V. coloradensis, species nos. 21-24. 

 c 4 . 0-5 teeth, never a basal fold ; cylindric or ovate 

 (pi. 10). 



Group of V. modesta, species nos. 25-28. 



c 5 . 0-4 teeth, no basal fold; no trace of a crest; 



cylindric, ribbed or with traces of ribs (pi. 9). 



Group of V. calif ornica, nos. 29-30. 



The keys to species are often insufficient for the identifica- 

 tion of critical or variable forms, but they are offered as better 

 than no guide. I have not been able to make differential 

 definitions of the groups of V. ovata, V. ventricosa, V. modesta 

 and V. calif ornica. 



Group of Vertigo ovata. 



Rather dark-colored, glossy shells usually having 7 to 9 

 teeth, never less than 5, the basal fold always present, but 

 often subcolumellar in position ; angular lamella present, often 

 an infraparietal also. Crest and auricle generally distinctly 

 developed. 



Key to species. 



1. Shell distinctly striate, the palatal callus, crest and 

 impressions behind the lip weak or wanting. Austro- 

 ripariau. V. rugosiila, no. 1. 

 Shell weakly or scarcely striate. 2. 



2. Last half whorl deeply impressed or constricted over the 

 palatal folds (pi. 8, fig. 14). Lamellae and lower palatal 

 fold long. Southern states. 3. 

 Last whorl only moderately or slightly impressed over 

 the lower palatal fold (pi. 6, fig. 2). 4. 



