1910.] NATURAL SCIENCES OF PHILADELPHIA. 51 



1. Species peculiar to the range: all forms of the genera Sonorella, 

 Oreohelix, Ashmunella and Holospira, 21 species with 14 subspecies. 

 These are the larger snails of the fauna, without exception larger and 

 heavier than any of the snails ranging also outside of the Chiricahuas. 

 The members of tnis group of forms have probably been isolated in 

 these mountains since the beginning of the present climatic cycle. 

 They are too heavy to be transported across the mesa by wind, and the 

 probability that they would be carried by birds or other accidental 

 means is so remote as to be negligible. All of them were apparently 

 derived from not more than six ancestral specific stocks ; the species 

 of Ashmunella and Holospira forming homogeneous groups probably 

 of common ancestry, while in Sonorella and Oreohelix the species fall 

 into two groups. 



2. Species having a distribution outside of the range: all of them smaller 

 than the preceding and many minute. 



(a) Alpine forms, mainly living above 7,500 feet, and elsewhere 

 found only in the Canadian zone of the Rocky Mountains northward. 

 Those found also in the Huachuca range are indicated by the letter H. 



Thysanophora ingersollimeridioncdis. Vertigo columbiana utahensis. 



Vitrina cdaskana, H. " modesta parietal is, H. 



Euconulus fulvus alaskensis, H. " coloradoensisbasidens. 

 Pyramidula cronkhitei, H. 



(6) Transition zone forms chiefly having an almost continental 

 distribution in that zone, also ranging into higher and lower zones. 



Zonitoides arbor ea, about 8,000 feet, H. 

 Cochlicopa lubrica, 6,000-8,000 feet, H. 

 Pupilla hebes, 7,500-8,000 feet, H. 

 Vertigo milium, 8,000 feet, H. 

 Succinea avara, about 6,500 feet, H. 



The species of groups (a) and (b) are forms which from their wide 

 distribution must be of considerable antiquity, all probably having 

 existed practically unchanged since before the initiation of present 

 climatic conditions in Arizona. The absence of any form of the Oreo- 

 helix strigosa group is remarkable, on account of the very wide distri- 

 bution of this Transition zone type in the Rocky Mountains. 



(c) Upper Sonoran species, most of them widely distributed in 

 the Southwest, some ranging into the Lower Sonoran. Those found 

 also in the Huachuca and Florida ranges marked with the letters H. 

 and F. 



