1910.] NATURAL SCIENCES OF PHILADELPHIA. 23 
Sonorella virilis, 6,000 to 9,000 feet. 
Oreohelix clappi, 6,000 to over 8,000 feet. 
Ashmunella chiricahuana, 6,000 to 8,500 feet. 
4 angulata, 6,000 to over 8,000 feet. 
Sonorella virilis leucura, S. micra, Ashmunella proxima, A. fissidens 
and their subspecies, and Holospira, seem, in their several areas, to 
range from low to as high as suitable cover and slope-exposure are 
found. Ashmunella esuritor, metamorphosa and duplicidens belong to 
the higher levels (where the flora is very different), while A. jerriss? 
has not been found over 6,500 feet, if so high as that. 
In general, the specially Canadian and Transition species seem to 
be more sharply limited in their range downward than the Upper 
Sonoran forms are in their extension upward. We attribute this 
as much to the difference in plant life as to any more direct climatic 
conditions. 
The Lower Sonoran zone, in this area, has no land molluscan fauna, 
but Physa and Lymnea occur in the cienega east of the Chiricahuas. 
V. SysTeMATIC DESCRIPTIONS OF SPECIES. 
Family HELICID Zi. 
This family comprises four genera in Arizona: Sonorella Pils., 
Oreohelix Pils., Ashmunella Pils. and Ckll., and Thysanophora Strebel. 
Ashmunella is confined to a comparatively small area in the southeastern 
corner of the territory; but the other genera extend to the northern 
border, but they are only locally distributed, and some or all may be 
absent over areas of hundreds of square miles. Ashmunella and 
Sonorella are Upper Sonoran genera. Oreohelix belongs to the Transi- 
tion zone, often extending into the Canadian (where it is usually 
dwarfed), and sometimes into the Upper Sonoran zone, where it 1s 
mainly represented by special species. 
The genera Ashmunella and Sonorella are curiously diverse in modes 
of racial differentiation. In Ashmunella the shell has been most 
modified. In series of allied forms from successive canyons of a single 
range the shells will show much greater divergence than the soft 
parts. This is well illustrated by the Huachucan series, which, with 
conspicuous differences among the shells, shows hardly any in the 
soft parts. In Sonorella, on the other hand, the shells from a series 
of successive canyons may show barely perceptible differences, but 
the genitalia have been so modified in detail that the species are 
instantly recognizable from these organs. The conditions in Sonorella 
