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PROCEEDINGS OF THE ACADEMY OF [Nov.-Dec.^ 



tained about 1.63 times in that of the shell, and in another locotype 

 (pi. IV, figs. 3-36) it is contained nearly 1.8 times. In the smaller 

 mouthed individuals the umbilicus is somewhat larger and less 

 covered, and the last whorl, viewed from above, is not so wide. We 

 have tried in vain to use these characters for a separation of the 

 series (some hundreds of shells); but while the extremes in size 

 of aperture appear quite distinct, the distinction could not be carried 

 through, as nearly every station supplied individuals with large, 

 intermediate and small apertures. 



The specimens from low in Sabino canyon usually have more 

 solid, thicker shells than those from higher; but this is not always 

 the case. 



It is a species of the arid mountains, confined to lower elevations 

 than S. marmorarius. 



Fig. 3. Sonorella sabinoensis, Sabino Canvon, genitalia, a, b, No. 109,098; c. 

 No. 109,097; d, No. 109,094. 



The smallest shells, diam. 19 mm., were found at Station 15, low 

 in Sabino canyon (about 4,000 ft.); but others up to 25 mm. diam. 

 occur in the same place. The largest, 27 mm. diam. are from 

 Station 9, 1913, the bluffs opposite Station 15. One of this lot is 

 figured, pi. IV, figs. 4-46. 



The degree of depression is variable in the same lot. Specimens 

 selected from a station on Vantana canyon measure: 



Alt. 14.5 diam. 20, mm. (largest). 

 " 13.2 " 25, " (most depressed). 



" 16.4 " 24.8, '' ( " elevated). 

 . " 12.2 " 20, " (smallest). 



Figures 5 to od are depressed and elevated shells from Bear canyon. 



