1910.] NATURAL SCIENCES OF PHILADELPHIA. 53 



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. 

 " angulata, 6,000 to over 8,000 feet. 



Sonorella virilis leucura, S. micro, Ashmunella proximo, 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. ferrissi 

 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 Lymncea occur in the cienega east of the Chiricahuas. 



V. Systematic Descriptions of Species. 

 Family HELIClDiE. 



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 is 

 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 



