1911.] NATURAL SCIENCES OF PHILADELPHIA. 185 



are visible on the base in front of the aperture in most of the shells. 

 The aperture is contracted less than in 0. y. profundorum and the 

 peristome is not thickened. The largest examples measure, alt. 8.2, 

 diam. 16 mm., the smallest alt. 8.3, diam. 14 mm. About 60 adults 

 examined. 



Fig. 18. Alt. 8.0, diam. 15.8 mm.; width of umbilicus 4.7 mm. 

 " 19. " 7.8, " 14.5 " " " 4.0 " 



" 19. " 8.7, " 14.2 " " " 4.0 " 



" 20. " 8.5, " 16.0 " " " 4.3 " 



" 21. " 8.0, " 15.5 " " " 4.3 " 



Cotypes are No. 103.236 A. N. S. P., collected by Ferriss and Pils- 

 bry, 1906. 



Similar shells occur on the upper slope at the same level, in a bay 

 of the rim, about a half-mile west, of Bass's Camp, on the southern 

 rim of the canyon (pi. XII, figs. 15, 16, 17). 



Fig. 15. Alt. 9.2, diam. 15.5 mm.; umbilicus 4.0 mm. wide. 



16. " 8.1, " 15.1 " " 4.1 " 



17. " 9.0, " 16.9 " " 4.9 " 





Oreohelix yavapai angelica. PL XII, figs. 22-25. 



On the Bright Angel Trail, at Grand Canyon, from 100 to 400 feet 

 below the rim, which has here an elevation of 6,866 feet, the shells 

 resemble 0. y. extremitatis in contour, except that the last whorl is 

 somewhat more inflated. The color is light brown, usually with a 

 brown band below the periphery, sometimes with another above, but 

 this is often wanting. It is thinner and larger than extremitatis, and 

 spaced spirals are more distinct, being well-developed on both the 

 base and upper surface. The embryonic whorls have faint spiral 

 lines. The first part of the neanic stage (up to at least 11 mm. diam., 

 with nearly 4 whorls in some individuals) bears spiral rows of cuticular 

 scales readily visible to the naked eye. There are about 8 spirals 

 above, 10 below the periphery on the last whorl. The last whorl is 

 but slightly deflexed in most examples, rarely (8 per cent.) more or 

 less deeply so, approaching fig. 25, which is an extreme individual. 



Fig. 22. Alt. 9.0, diam. 17.0 mm. ; width of umbilicus 4.5 mm. 



" 17.0 " " " 4.9 " 



" 17.9 " " " 4.8 " 



" 16.0 " " " 3.8 " 



Individuals with deeply descending last whorl occurred chiefly at 

 the lower level. 



