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 dextroversa, 

 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, " 1.6 " " 7i 



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 w r as associated 

 with form dextroversa 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 w T ith 7 whorls to 3.7 mm. with 8 

 whorls. Most of them are triplicate, the columellar lamella and lower 



