196 PROCEEDINGS OF THE ACADEMY OF [March, 
At about the same elevation about 4 or ? mile west of Bass’s Camp 
a similar specimen of dextroversa was taken. 
Pupilla syngenes avus n. subsp. Fig. 9. 
Shell sinistral, the last whorl deviating tangentially and ascending; 
teeth deeply immersed; parietal lamella much longer than in P. s Ae 
or dextroversa, about a half-whorl long. 
Length 5.2, diam. 1.8 mm., whorls 103. 
ce 4.3, ce 7 ce “e 94. 
‘cc 4. 0, cc 7 ‘“ gt. 
Types No. 94,220 A. N. S. P., from upper slope of the Grand 
Canyon along the Mystic Fe or Bass Trail, about 200 feet below 
the rim, Station 2; abundant with P. s. dextroversa. . 
Fig. 9.—Pupilla syngenes avus, Cotypes. Lengths 5.2, 4, 4 and 4.2 mm. 
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 associated with about 
an equal number of P. s. dextroversa of about the same size, we at first 
were disposed to think them all one race in which the shell was indiffer- 
ently dextral or sinistral; but on closer study it appears that the 
dextral forms never have the last whorl and aperture abnormal nor 
are the teeth so deeply immersed, or the parietal lamella so long, 
while almost every sinistral shell collected in this colony is markedly 
distorted. It seems, therefore, that although the two forms are of 
common origin and live together, the different direction of the coil 
probably prevents interbreeding, thus segregating the sinistral stock, 
which in this colony is now in a late stage of senile degeneration. 
