1910.] 



NATURAL SCIENCES OF PHILADELPHIA. 



89 



Alt 9.7 



Diam 15 



Whorls 5i 



Alt 



Diam.... 

 Whorls. 



10 

 14.2 



In these shells the peripheral angle is about as in Cave Creek types, 

 but the base is smoother, 

 the striation nearly 

 effaced, and spiral striae 

 are wanting or very rarely 

 a few may be faintly 

 seen under the keel. 

 Shells from Stations 

 1,2,6,7,8, 12 agree with 

 those from 14. These 

 stations are on rather 

 steep slopes with gener- 

 ally northern exposure, 

 and from somewhat 

 over 6,000 to about 7.000 

 feet elevation. The 



distribution over this 

 area is nearly or quite 

 continuous. 



At Station 3, just over 

 the crest of the ridge, on 

 the Pinery Canyon side, 

 probably a little over 

 7,000 feet elevation, the 

 shells are smaller, 11.8 

 to 13 mm. diameter; 

 otherwise similar. This 

 station is very high and 

 exposed, on a sunny 

 slope, hence extremely 

 dry and arid; but the 

 following record shows 

 that mere elevation is 

 not a factor of impor- 

 tance. On the south side 

 of White Tail Creek, only 



Fig. 13.— O. c. obsolete P. and F. A, White Tail, 

 Station 14; B,C, Limestone Mountain. Drawn 

 10 and 11. 



to same scale as figs. 



