MAMMALS OF THE MEXICAN BOUNDABY. 



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 vertebrse, 

 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 apically. The dentition is very heavy. (Fig. 112.) 



Fig. 112.— Sigmodon hispidus akizon^e. Skull of type. a. dorsal view; 6, ventral view; 



C LATERAL VIEW. 



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

 Sigmodon 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 Meaens, Proc. U. S. Nat. Mus., XX, 1898, p. 504 (advance 



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



See. 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. Soo. 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. Am.). 



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 



