MAMMALS OF THE MEXICAN BOUNDARY. 451 



bushy, yellowish brown hairs on both surfaces, more sparingly out- 

 side. Pelage coarser and more hispid than that of any other form of 

 this species on the Mexican Line. Length, 320 mm.; tail vertebrae, 

 120; ear from crown, 18; hind foot, 36. Skull, 40 by 22 mm. in 

 greatest dimensions. (See also p. 453.) The skull is high at the 

 interorbital region, sloping down in either direction; nasal bones 

 compressed ajiically. The dentition is very heavy. (Fig. 112.) 



a b c 



Fig. 111'.— Sigaiodon hispidus arizon.e. Skull of tvpe. a. dorsal view; b, ventral view; 



(• LATERAL VIEW. 



Remarks. — This is nmch the largest representative of the genus 

 Sigmodori found within the United States. It is known only from the 

 Verde River, in central Arizona; from the San Pedro River, at Fair- 

 bank, in southern Arizona; and from Granados, on the Yaqui River, 

 in Sonora, Mexico. 



SIGMODON HISPIDUS EREMICUS Mearns. 

 "WESTERN DESERT COTTON RAT, 



Sigmodon hispidus eremicus Mearns, Proc. U. S. Nut. Mus., XX, 1898, p. 504 (advance 



sheet issued Mar. 5, 1897; original description). — Miller and Rehn, Proc. Bost. 



Sue. Nat. Hist., XXX, No. 1, Dec. 27, 1901, p. 90 (Syst. Results Study N. Am. 



Mam. to close of 1900); XXXI, Aug. 27, 1903 (Syst. Results Study N. Am. Mam. 



during the years 1901 and 1902). — Bailey, Proc. Biol. Soc. Washington, XV, 



p. 107, June 2, 1902 (Synopsis of the North American Species of Sigmodon). 

 [Sigmodon hispidus] eremicus, Elliot, Field Col. Mus., Zool. Ser., II, 1901, p. 145 



(Synop. Mam. N. Am). 

 [Sigmodon] hispidus eremicus, Elliot, Field Col. Mus., Zool. Ser., IV, 1904, p. 227 (Mam. 



Mid. Ain.). 



Type-locality. — Colorado River bottom, 30 miles below Monument 

 No. 204, in Sonora, Mexico. (Type, skin and skull, Cat. No. 60319, 

 U. S. National Museum.) 



Geographical range. — Inhabits marshes, alfalfa fields, and brushy 

 ground in the vicinity of streams in the Western Desert Tract. 



Description. — Size medium. Coloration pallid and yellowish. Up- 

 per surface yellow-brown mixed with gray and darker brown; sides 

 and rump tinged with ochraceous. Under surface white, the gray 

 undercoat appearing between the hairs. Feet grayish white. Tail 



