170 PUPILLA, AMERICAN. 



narrowly expanded. The parietal lamella is slightly over 

 one-fourth of a whorl long; the columellar lamella small and 

 deeply immersed, and the lower palatal nodule well developed 

 or weak, but invariably present in adult shells. 



Length 4, diam. 1.7 mm. ; 9 whorls. San Rafael. 



Length 3, diam. 1.6 mm. ; 7Vi> whorls. San Rafael. 



Length 4.5, diam. 1.8 mm. ; 10 whorls, Grand Canyon. 



Length 3.7, diam. 1.8 mm. ; 9 whorls. Grand Canyon. 



FIG. 2. P. s. dextroversa P. & V. San Rafael, N. M. 



NEW MEXICO: San Rafael* (type loc., Ashmun), and Grant 

 (Baily), Valencia Co. ARIZONA: Holbrook * (Ashmun); 

 Grand Canyon, Bright Angel Trail,* and just below the 

 south rim near Bass Camp (Ferriss & Pilsbry), and in Stone 

 House Gulch, Kaibab Plateau* (Ferriss & Daniels). COLO- 

 RADO: Tolland, Gilpin Co. (Cockerell) and Eldora, Boulder 

 Co. (Henderson). 



At localities marked with a * it occurred in association 

 with sinistral P. syngenes. 



This form differs from P. muscorum by the shape and num- 

 ber of whorls of the shell, and the longer parietal lamella. 



P. s. dextroversa differs from P. syngenes only by the dex- 

 tral coil. Since dextral forms are doubtless the more primi- 

 tive in Pupilla, it is evidently dextroversa which perpetuates 

 the original stock of the species. Perhaps it might be ranked 

 as a mutation rather than a subspecies. In half of the local- 

 ities given above, only dextral shells were found ; but at the 



