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BULLETIN 56, UN [TED STATES NATIONAL MUSEUM. 



PEROMYSCUS TORNILLO Mearns. 



TORNILLO MOUSE. 



Peromyscus tornillo Mearns, Proc. U. S. Nat. Mas., XVIII, 1890, pp. 445, 446 (p. 3of 

 advance sheets issued Mar. 25, 1890: original description). — Miller and Ki.iin, 

 Pmc Bost. Soc. Nat. Hist., XXX, No. 1, Dec. 27, 1901, p. 87 (Syst. Results 

 Study N. Am. Mam. to close of 1900). 



[Peromi/scus] tornillo, Elliot, Field Col. Mus., Zool. Ser., II, 1901, p. 12G (Synop. Mam. 

 N.Am.); IV. 1904, p. 188 (Mam. Mid. Am.). 



Type-locality. — Rio Grande bottom lands, 6 miles above El Paso, 

 Texas. (Type, skin and skull, Cat. No. |fH4>U. S. National Museum.) 



Geographical range. — An inhabitant of the Eastern Desert Tract. 

 Known only from the bottom lands of the upper Rio Grande, living 

 in forests of " tornillo " or screw bean (Prosopis odorata). There are 

 specimens in our collection from Texas, New Mexico, and Chihuahua. 



Fig. 84.— Peromyscus tornillo. Skull, a dorsal view; ''.ventral view; c, lateral view. 



Description.— A large, stout species; ears and tail well haired, the 

 latter sharply bicolored; soles densely pilose posteriorly. Upper sur- 

 face light broccoli brown; ears and upper side of tail hair brown; feet 

 and under parts pure white. Length, 190 mm.; tail vertebrae, 90; 

 ear above crown, 12; hind foot, 23. Skull, 29 by 14.5. 



Cranial and dental characters. — The skull of this mouse (fig. 84) is 

 at once distinguished from all other Texas mice of this genus by its 

 larger size. The animal bears a superficial resemblance to the /\ 

 arizonse, described by Dr. J. A. Allen, from Fairbank on the San 

 Pedro River, in Arizona. Externally it is distinguished from that 

 species by its paler coloration, slightly smaller ears, and stouter body. 

 The largest skulls of P. arizonx equal the average size of P. torniMo, 

 but the teeth are smaller. The shape, however, is different. In both 

 of these species the rostral portion is long and high, this character suf- 

 ficing to distinguish them from any of the forms of P. sonoriensis. 

 The skull of P. tornillo is low and squarish, with the superior profile 

 but slightly arched, and its zygomatic arches standing strongly out in 

 front, as sharp elbows at right angles to the cranial axis. The upper 



