MAMMALS OF THE MEXICAN BOUNDARY. 



371 



ONYCHOMYS PALLESCENS (Merriam). 

 EASTERN DESERT GRASSHOFFEE MOUSE. 



Onychomys melanophrys pallescens Mbeeiam, North America Fauna, No. 3, Sept. 11, 



1890, pp. 61, 62 (original desofiption). — Miller and Rehn, Proc. Bost. Soc. Nat. 



Hist., XXX, No. 1, Dec. 27, 1901, p. 67 (Syst. Results Study N. Am. Mam. to close 



of 1900). 

 [Onychomys leucogaster] pallescens Elliot, Field Col. Mus., Zool. Ser., II, 1901, p. 121 



(Synop. Mam. N. Am.). 

 0[nychomys] m[elanophrys] pallescens, Elliot, Field Col. Mus., Zool. Ser., IV, 1904, 



pp. 165 and 166 (Mam. Mid. Am.). 



Raton of the Mexicans. 



Type-locality. — Hopi pueblos, Apache County, Arizona. (Type, 

 skin and skxill, No. ||||, collection of Dr. C. Hart Merriam.) 



GeograpTiical range. — Sonoran zone 

 of the desert basins of the upper Rio 

 Grande and Little Colorado rivers — 

 the Eastern Desert Tract. 



Description. — Smaller than 0. long^ 

 ipes or 0. melanophrys. Average 

 measurements of six adults: Length, 

 159 mm.; tail vertebrae, 51 (to end of 

 pencil, 54); ear above crown, 15; ear 

 above notch, 18.5; length of hind 

 foot, 23. Skull (fig. 61a), 30 by 16. 

 Coloration, very pale; above, pale 

 annulated hairs, becoming paler and 

 grayish on the head and brighter 

 tawny cinnamon, but slightly mixed 

 with black-tipped and black cinnamon on the flanks and rump ; palest 

 specimens, light fawn color or 6cru drab above; under surface, feet, 

 and end of tail white ; ears bufly white, with a large seal-brown spot 

 on anterior border of convex surface and conspicuous lanuginous 

 tufts at anterior base; dusky stripe on upper side of tail, obsolete. 

 Mammse: P}, A. g, I. | =3 pairs. 



This desert mouse was found by us only from El Paso, Texas, to the 

 Mimbres Valley, near Monument No. 15 of the boundary. From that 

 point westward to the San Bernardino Valley, at Monument No. 77, 

 we found no large species of Onychomys. The San Bernardino form, 

 which we refer to 0. melanophrys, is the darkest of the group, excepting 

 Onychomys fuliginosus Merriam, from the pinon and cedar belt and 

 the black lava beds between San Francisco Mountain and the desert 

 of the Little Colorado, which has a dark, almost blackish, coloration, 

 unique in the genus. 



FiG.Cl. — Onychomys PALLESCENS. a, Skull; 

 b. Lower molars, c. Upper molars. 



