1911.] NATURAL SCIENCES OF PHILADELPHIA. 181 



the largest, alt. 12, diam. 17.2, umbilicus 2.5 mm. (F. and D. 1909). 

 Some of- these shells are the largest taken up to this time, exceeding 

 the types. The shoulder-band is faint or wanting on some shells. 



(10) Station G: White Creek, about 1 mile above its confluence 

 with Shinumo Creek (PI. XII, figs. 26-28). Seven per cent, of the 

 shells taken show a chestnut band. In the rest there is an ill-defined 

 whitish band in its place. Bandless shells are rare in all other localities. 

 The aperture is also more ample in this lot, somewhat trumpet-shaped, 

 the lip is rather more thickened and rusty, and the parietal callus is 

 generally thick at the edge. 



Alt. 10, diam. 17.0, umbilicus 2.6 mm. ; aperture 8.8 x 10.0 mm. 

 " 10, " 16.2, " 2.1 " " 8.2 x 9.5 " 



" 9, " 15.2, " 2.25 " " 8.0 x 8.8 " 



The genitalia of a specimen of this lot are figured, fig. SB. 



(11) Muav Box, Station 9, elevation 4,000 feet (F. and D., 1909). 

 Diam. 15-16 mm. All taken have the shoulder-band. 



(12) Station H: Mojave Amphitheatre below the red-wall sand- 

 stone (west side of Muav Canyon, near Button's Point). The shells 

 are all banded, measure 14 to 16 mm. diameter, and do not seem to 

 differ from those taken on the Shinumo at a much lower elevation. 

 At this point the authors made a dry camp in 1906, being unaware that 

 there was water a few miles beyond. In 1909 Ferries and Daniels 

 took a fine lot of unusually large and dark colored Sonorellas at Station 

 107, about two miles farther up Muav Canyon, but they were lost 

 before reaching home. 



(13) Station 104, 6,700 feet, and Station 9, 7,500 feet, east side of 

 Powell Plateau (west of Muav Wash). Small, 13.5 to 14 mm. diam.; 

 banded; aperture dilated, as in the shells described under (10). This 

 colony and those following were taken by Ferriss and Daniels, 1909. 



(14) Station 5, east of Muav Canyon, near the Kaibab Saddle, 

 6,717 feet. Small shells, diam. about 13.5 to 15 mm., with the mouth 

 less dilated than in the preceding lot, nearly normal. All are banded. 



(15) Station 25, west side of Powell Plateau, 6,700 feet. The 

 shells are small, diam. about 14 mm., with thickened lip and somewhat 

 dilated mouth, as in Nos. (13) and (19). 



(16) At Station 23, Horse Tank Canyon, on the west side of Powell 

 Plateau, 7,000 feet, the shells are like those from No. (12). Some 

 bandless individuals were also taken. 



(17) Station 101, north end of Powell Plateau, 6,700 feet. Only 

 dead and bleached shells, normal in shape. 



(18) Station 100, third amphitheatre north of the Kaibab Saddle, 



