MAMMALS OF THE MEXICAN BOUNDARY. 



373 



of the form 



crown, 14.7; ear above notch, IS. 2; length of hind foot, 22.5. Skull, 

 29 by 16 mm. (For teeth see fig. 62.) Color above, dull tawny 

 cinnamon well mixed with black-tipped hairs on the back, and brightest 

 on the sides and rump; eye encircled by a narrow black ring; under 

 parts, feet, and end of tail, pure white; tail with a dark drab stripe 

 on basal three-fourths of upper side; ears dusky, mixed with hoary 

 apically, with a black spot on anterior border of outer surface, and 

 with lanuginous tufts inconspicuous. 



The foregoing description is based on specimens from the Mexican 

 border, on the San Pedro River, Arizona. A series of more than thirty 

 was obtained from that general region (San Pedro and Santa Cruz 

 valleys) and from the Verde Valley in central Arizona. These speci 

 mens represent the extreme degree of development 

 described from Utah, which Doctor Merriam has 

 named melanopTirys , and differ from the type in being 

 larger and darker, with the upper surface duller, 

 more grayish drab, with the flanks and rump less tawny 

 cinnamon. 



Half-grown young are smoke gray, with hoary tips 

 to the ears and a black spot on their anterior band. 

 They are almost indistinguishable from the young of 

 0. longipes, though a trifle paler. When three-fourths 

 grown the coloration is very similar to that of the 

 gray phase of Peromyscus texanus. Young adults are 

 dull drabish, without the bright cinnamon tint of 

 adults. The changes of color dependent upon the 

 several stages of age and molt may be graded as follows: (1) Gray, 

 fading later to smoke gray; (2) drab gray, (3) broccoli brown, (4) dull 

 tawny cinnamon. 



Remarks. — As usual, the form of this species from the San Bernar- 

 dino Valley (Monument No. 77) is much darker than elsewhere on the 

 Mexican line, and may represent a distinct geographical race in the 

 Yaqui Valley. 



Hahits.—lA^e the other species of OnycJiomys, the black-eyed 

 grasshopper mouse likes open country, where it digs its burrows 

 straight down into the level ground, or, more often, selects a little 

 bank, such as the side of a ditch or arroyo, and digs a slanting 

 burrow. At Fort Verde the gardeners sometimes opened their nests 

 when plowing; and on one such occasion a mother ran out with four 

 small young attached to her teats. Aside from similar accidents, I 

 have never seen one out of its burrow during the daytime, and suppose 

 this mouse to be strictly nocturnal. 



Fig. 62. — Onycho- 

 mys melano- 

 PHRYS. a. Lower 

 molars; b. Upper 



MOLARS. 



