PUPILLA, AMERICAN. 155 



much in common with hebes. P. muscorum is sometimes 

 thin-lipped, closely approaching fabes. P. hebes and P. syn~ 

 genes occur in both dextral and sinistral forms. Colonies 

 containing albinos have been noted in muscorum, syngenes, 

 hebes and blandii. They form an intricate complex of races, 

 the affinities of which may be represented by a diagram. 



sonorana blandii muscorum syngenes 



I I 



pithodes hebes 



P. sterkiana stands apart from this complex of forms, 

 being strongly characterized by the sculpture of both embry- 

 onic and later whorls, the former resembling those of Primi- 

 pupilla. 



Key to American Species. 



1. Shell rib-striate, the embryonic whorls reticulate-granose ; 



Lower California (Section Striopupilla-) . 



P. sterkiana, no. 1. 



Shell minutely striate or smoothish (Section PupiUa 

 proper) 2. 



2. Spire slightly wider above than below; parietal lamella 



long; 8-10 whorls P. syngenes, no. 6. 



Spire not wider above ; whorls less numerous 3. 



3. Aperture having three well-developed teeth, the palatal 



fold somewhat long 4. 



Teeth wanting or, when present, small, the palatal fold 

 tubercular 5. 



4. Length 3.2 to 3.75 mm P. blandi, no. 3. 



Length 2.5 to 3.25 mm. ; palatal fold long ; last whorl much 



flattened behind the crest P. sonorana, no. 4. 



5. Lip typically thickened within, with a whitish crest ex- 



ternally ; teeth small or wanting P. muscorum, no. 2. 



Lip thin; crest colored like the shell, often low, scarcely 

 noticeable ; typically toothless ; Arizona to Idaho. 



P. hebes, no. 5. 



