Mammals of the Sonoran Region. 27 



Cariacus Mephitis 

 Antilocapra T Fclis 



(Ynomys Lynx 



Sitomys * Scapanus 



Neotoma Blarina 



Thorn omys Atalapha 



T Procyon Vesperugo 



Taxidea Vespertilio 



The genera Sitomys, Mephitis, Lynx, Atalapha, Vesperugo, and 

 Vespertilio range well north in the Boreal Zone, where each is 

 represented by a single species. In the Sonoran Zone, on the 

 other hand, these same genera reach their maximum develop- 

 ment and are represented by numerous species. 



Besides the genera above enumerated, a number of subgenera 

 belong to the Sonoran Region. Among these are Neosdurus and 

 Parasciurus (subgenera of Sciiirus), Xerospermophilus,^ Ammosper- 

 mophilusl and Ictidomys (subgenera of Spcrmophilus'), Pitymys, 

 Pcdomys and Neofiber (subgenera of Arvicola), and Chsetodipus (a 

 subgenus of Perognathus, which is almost entitled to rank as a 

 full genus). 



The Sonoran 1 Region may be divided by temperature into 

 two principal transcontinental zones, (a) Upper Sonoran, and (6) 

 Lower Sonoran ; and each of these in turn may be subdivided 

 into arid and humid divisions. 



The gray fox, Urocyon, ranges over both Upper and Lower 

 Sonoran from Atlantic to Pacific ; and pocket gophers of the 



*The generic name Hesperomys being untenable, Allen has recently 

 substituted for it the name Vesperimus, proposed by Coues as a subgenus 

 in 1874 (Bull. Am. Mus. Nat. Hist., Ill, No. 2, June, 1891, pp. 291-297). 

 Vespcrimus is antedated by Sitomys of Fitzinger, proposed in 1867, and 

 based on Gapper's Cricetus myoides from Lake Simcoe, Ontario, Canada 

 (Sitzungsber. math. nat. Classe, K. Akad. Wiss. Wien, LVI, 1867, p. 97). 

 Gapper's Cricetus myoides is the common white-footed mouse of southern 

 Ontario and northern New York, which therefore becomes the type of 

 the genus. 



t Xerospermophilus, subgen. nov., proposed for Spermophilus mohavensis 

 (type) and the allied species of the S. spilosoma group. 



$ Ammospermophilus, subgen. nov., proposed for Spermophilus leucurus 

 (type) and allied species. 



\ The great Lower Sonoran Zone may be split lengthwise (in an east 

 and west direction) into two belts which have not yet been thoroughly 

 differentiated. 



