196 



PROCEEDINGS OF THE ACADEMY OF 



[March, 



At about the same elevation about \ or f 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. syngenes 

 or dextroversa, about a half-whorl long. 

 Length 5.2, diam. 1.8 mm., whorls 10^. 

 4.3, " 1.7 " " 9i 



4.0, " 1.7 " " 9i 



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, 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, Ave 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. 



