194 PROCEEDINGS OF THE ACADEMY OF [March, 
In Pupilla it is obvious that dextral forms are the more primitive, 
the sinistral forms derived from them. P. syngenes deztroversa, 
therefore, perpetuates the original stock of the species, of which 
P. syngenes is a divergent branch. 
P. s. dextroversa (fig. 6) is subcylindric, a little wider near the upper 
end. The last whorl is flattened laterally, with a strong rounded 
crest and a deep constriction behind the lip, which is thin and very 
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. The size varies. 
Length 4, diam. 1.7 mm., whorls 9. 
“ 3, 7 16 “ a 74 q 
P. s. dextroversa differs from P. blandi by its larger, comparatively 
narrower and more cylindric shape, and the greater number of whorls. 
The two forms were doubtless of common ancestry. 
Types of P. s. dextroversa are No. 79,460 A. N.S. P., from San Rafael, 
N. M., collected by E. H. Ashmun. Also taken at Holbrook, Ariz. 
(Ashmun), at Grants, N. M. (Joshua Baily, Jr., and Albert Baily), and 
in the Grand Canyon of the Colorado, see below. 
The specimens from San Rafael and Holbrook are mirror images 
of the sinistral P. syngenes found with them. At Grants very few 
were found, no sinistral ones with them. 
It appears, therefore, that some colonies of the older dextral form 
occur unmixed with sinistral, and sometimes the sinistral form is 
found unaccompanied by dextral. 
Our records of P. syngenes in the Grand Canyon follow. 
North of the Grand Canyon Ferriss and Daniels took P. syngenes 
at Station 25, Powell Plateau; Stations 100, 5 and 7 on the Kaibab- 
Powell saddle; and at Station 66, Kaibab Plateau. It was associated 
with form deztroversa at Stations 5 and 7, near the ‘Stone House.” 
Grand Canyon at the Bright Angel Trail, about 100 feet below the 
rim. P. syngenes and P. s. dextroversa, 19 of the former, 12 of the 
latter, normal in shape, most adults having a palatal tubercle. P. 
syngenes was also taken near the base of the cross-bed sandstone, one 
specimen. 
Mystic Spring or Bass Trail. At Spectacle Cove (Station A), on 
the Oreohelix talus, below the cross-bed sandstone, 103 examples 
of P. syngenes from half-grown to adult were taken, all of them sinis- 
tral. Adults vary from 3 mm. long with 7 whorls to 3.7 mm. with 8 
whorls. Most of them are triplicate, the columellar lamella and lower 
