302 Univi rsity of California Publications in Zoology [Vol. 12 



The previously described forms of Microdipodops are: M. mega- 

 cephalus (C. H. Merriam, 1891, p. 116), type locality Halleck, Elko 

 County, Nevada; M. megacephalus oregonus (C. H. Merriam, 1901, p. 

 127), type locality Alvord Desert, Harney County, Oregon ; .1/. /mil it! its 

 (C. H. Merriam, 1901, p. 127), type locality Carson Sink, near Still- 

 water, Churchill County, Nevada; 31. californicus (C. H. Merriam, 

 1901, p. 128). type locality Sierra Valley, near Vinton. Plumas County. 

 California. 



Microdipodops polionotus. new species 

 Mono Kangaroo Mouse 



Type. — Male adult, no. 17031, Mus. Vert. Zool. ; McKeever's Ranch, 

 two miles south of Benton Station, Mono County, California, altitude 

 5200 feet; July 10, 1912. Collected by C. D. Holliger; orig. no. 184. 



Diagnostic Characters. — Nearest like Microdipodops pallidus in 

 general appearance, but coloration paler, decidedly more ashy in tone. 

 and white areas emphasized in brilliancy ; pelage notably shorter, less 

 lax and fluffy; general size less, and tail decidedly shorter; skull similar 

 to that in pallidus and megacephalus, but auditory capsules slightly 

 less inflated, particularly less protuberant behind. 



Coloration of Type. — Above, cartridge buff (of Ridgway's Color 

 Standards and Color Nomenclature, 1912), with the hairs minutely 

 black-tipped especially on the rump ; sides of face and rump least 

 buffy, presenting a distinctly ashy tone; underfur a pale tint of gray, 

 number 7 ; dorsal side of tail cartridge buff proximally, becoming 

 gradually dusky-hued towards tip ; lower surface of tail and feet, 

 white; whole lower surface of body brilliant white, abruptly contrasted 

 with dorsal color along sides ; some of whiskers black, and others, the 

 longer posterior ones, white ; ears like back in tint, but with a silvery 

 white upper rim, a conspicuous snowy white spot at inferior base, and 

 an even larger white patch just behind. 



Measurements. — Of type, total length 145 millimeters, tail verte- 

 brae 80, hind foot 24, ear from crown 9 ; average of seven adults, total 

 length 148. tail vertebrae 82, hind foot 23.7, ear from crown 7.6. 



Comparative Remarks. — The new species differs from all those pre- 

 viously described in extreme pallor of coloration. The contrast with 

 californicus is particularly great, the dorsal color in that form being 

 strongly brownish, approaching tawny-olive in fused tone. Polionotus 



