PUPILLA, AMERICAN. 



171 



two in Colorado only single shells were taken. In a few 

 colonies, so far as our information goes, the dextral form 



FIG. 3. P. s. dextroversa P. & V. Bass Trail, Grand Canyon, about 200 ft. 



below the rim. 



Lengths 4.5 and 3.76 mm. 



occurs as a pure race, and many more colonies are of purely 

 sinistral shells. 



The Colorado records quoted from Cockerell and Hender- 

 son are widely detached from those in New Mexico and Ari- 

 zona. All of the material from the latter states has been ex- 

 amined by the w r riter. 



P. syn genes avus Pils. & Ferr. Fig. 4. 



Shell sinistral, the last whorl deviating tangentially and 

 ascending ; teeth deeply immersed ; parietal lamella much 

 longer than in P. syngenes or dextroversa, about a half -whorl 

 long. 



Length 5.2, diam. 1.8 mm., whorls 



Length 4.3, diam. 1.7 mm., whorls 



Length 4.0, diam. 1.7 mm., whorls 9y 2 . 



Types no. 94,220 A. N. S. P., from upper slope of the Grand 

 Canyon along the Mystic Spring or Bass Trail, about 200 feet 

 below the rim; abundant with P. s. dextroversa. 



The special characters of this race, being those of senility, 

 are unequally developed in different individuals. The figures 

 give a fair idea of the variations. Finding these shells asso- 



