46 PROCEEDINGS OF THE ACADEMY OF [Feb., 
can fauna as full as circumstances permitted. In many of the canyons 
we have endeavored to locate the individual snail colonies with suffi- 
cient detail to insure their recognition by subsequent observers, so 
that their further evolution may be followed. Large areas still 
remain to be explored, and neither author has had time to fully study 
the material collected. 
The first record of mollusks from the Chiricahuas was made by 
Dr. R. E. C. Stearns, who in 1890 describes specimens of Holospira 
arizonensis,* collected by Mr. Vernon Bailey for the U. 8. Department 
of Agriculturefat Dos Cabezas, in the western foothills of the Dos 
Cabezas Mountains. In 1895 Dr. W. H. Dall described Polygyra 
chiricahuana and subsequently (1897) he reported Pyramidula striatella, 
Thysanophora ingersolli and Zonitoides arborea,* all from Fly’s Park 
in the central Chiricahuas, collected by Dr. Fisher. No other species 
were known from the range prior to the first visit by Mr. Ferriss in 
February, 1904. Numerous new species were found during this brief 
visit, notwithstanding the unfavorable season. In November, 1906, 
both of us collected in the range, exploring the principal canyons from 
Buckeye in the north to Cave Creek and the parks about its head. 
In November, 1907, Messrs. Ferriss and L. E. Daniels spent two 
weeks in the Chiricahuas, and in 1908, from September 20 to November 
15, Ferriss continued the work of exploring the southern canyons. 
I. ConpDITIONS DETERMINING THE ISOLATION OF SNAIL COLONIES. 
The faunas of the several mountain ranges of southern Arizona 
are separated one from another by the intervening nearly level mesa, 
where snails are absolutely wanting and cannot exist. This is due not 
alone to their greater aridity, higher temperature and xerophytic 
flora, but chiefly we believe to the absence of rocks, in the interstices 
of which snails might burrow below the dry surface to depths where 
a certain amount of moisture is retained. The mesa forms a barrier 
as impassable to land snails as an equal expanse of sea; and can be 
surmounted only by minute forms light enough to be transported by 
the wind. During the existence of the present conditions, which 
probably were initiated in the Pliocene, the larger snails of each range 
have been absolutely isolated. 
Owing to the general north and south trend of the ranges, the main 
canyons run eastward or westward, thus exposing a very hot slope 
3 Proc. U. S. Nat. Museum, XIII, 1890. “ 
4 Proc. U. 8S. Nat. Museum, XVIII, 1895, and XIX, 1897. 
