MAMMALS OF THE MEXICAN BOUNDARY. 389 



PEROMYSCUS SONORIENSIS BLANDUS Osgood. 

 CHIHUAHUA PLAINS MOUSE. 



Peromyscus sonoriensis h/nm/us ()s<;<><>i>, Proc. Biol. Soc. Washington, XVH, p. 56, 



Mar. 21, L904. 

 Eesperomys leucopus texanus, Mearns, Bull. Am. Mus. Nat. Hist., II, pp. 285-287, 



Feb. 21, 1890 (Oklahoma). 

 Peromyscus texanus, Mearns, Proe. Q. S. Nat. Mus., XVIII, 1896, p. 146. Miller 



and Rehn, Proc. Bost. Soc. Nat. Hist. XXX. No. I. Dec. '-'7. 1901, p. M (Syst. 



Results Study N. Am. Mum. to close of 1900). 

 \[Peromyscus] texensis, Elliot, Field Col. Mus.,Zool. Set., II, I'.mii , p. l30(Synop.Mam. 



N. Am.); IV, 1904, p. 186 (Mam. Mid. Am.). 



Type-locality. -Escalon, Chihuahua, Mexico. 



Geographical range. Sonoran Zone of the Eastern Desert Tract. 

 From the Quitman Mountains, Texas, west to the Ilaeliita Mountains, 

 New Mexico, and southward into Mexico; intergrading with Pero- 

 myscus sonoriensis nebrascensis to the northward. 



Description.— An adult male (No. 21177, U.S.N.M.) taken 50 miles 

 west of El Paso, on the Mexican Line, March 21, 1 s « » ii , is in winter 

 pelage. Size small. Length, 160 mm. ; tail vertebrae, 68; ear above 

 crown, 14.5; length of hind foot and claw, 21.5. Ears small, with a 

 lanuginous tuft at anterior base; tail short, hairy, and sharply bicolor, 

 but without a distinct pencil of hairs at tip. Color above ochraceous 

 drab, grayish anteriorly, deepening laterally and posteriorly to ochra- 

 ceous cinnamon, everywhere finely lined with black, most thickly in 

 the vertebral area; feet and under surface pure white ; ears seal brown 

 with a mixture of hoary on edges and within, and long-haired in ;i 

 patch occupying the anterior portion of the convex surface; tail 

 white, with a narrow stripe of clove brown on upper side, extending 

 from base to tip. Soles densely hairy from the heel to the tubercles. 

 The young are gray above, white below, with a conspicuous slate- 

 black patch on the anterior half of the convex surface of the ear. Of 

 22 grown specimens taken between the Rio Grande and the San Luis 

 Mountains on the Mexican Line. March 21 to June l,and one in Sep- 

 tember, but three were in the rufescent pelage, the rest varying from 

 pale smoke gray to drab gray, several being more or less interme- 

 diate between the grayish and ochraceous phases of coloration, which 

 depend to some extent upon season. 



Crania/ diameters. — As the members of the Peromyscus sonoriensis 

 group have long been considered to be specifically identical with 

 Peromyscus leucopus (Rafinesque), I will compare one of the forms of 

 P. sonoriensis, namely, /'. s. nebrascensis, with that species: I am 

 able to detect but slight differences between series of skulls of P. 

 leucopus from the District of Columbia. Lexington (Kentucky) , and 

 various other eastern localities, and series of the same species 

 from Fort Snelling and Elk River, Minnesota. Comparing series 

 of skulls of /'. leucopus from the forested areas of >oiithern 



