296 University of California Publications in Zoology. \Vou-> 
The ratio of the zygomatie width to the greatest length is 
seen to be practically the same in the two forms, that of the 
squamosal width to the greatest length being slightly larger in 
desertorum. A constant difference between the two is shown by 
the ratio of the height of the cranium at the auditory bullae to 
the greatest length. In nevadensis this ratio is two to three per 
cent. greater than in desertorwm. 
The table shows individual and sexual variation. Skulls of 
the females average smaller than those of the males except as 
regards two measurements. In nevadensis the interorbital con- 
striction averages the same in males and females, being, in 
desertorwm, less in the females than in the males. The maxillary 
tooth-row is in nevadensis longer in females than in males; but 
the reverse is true of desertorum. That sexual variation in the 
two species is not exactly parallel is shown also by the fact that 
whereas in nevadensis the ratios of the zygomatic width, squa- 
mosal width and height of cranium at bullae to the greatest 
length are respectively greater in thé females than in the males, 
in desertorum the opposite is the case. 
Disrripution.—The Nevada wood rat was collected at the 
following loealities: Virgin Valley, 9 specimens; Quinn River 
Crossing, 1 specimen; Mouth of Big Creek, Pine Forest Moun- 
tains, 3 specimens; and Mouth of Alder Creek, Pine Forest 
Mountains, 2 specimens. Thus the range of the animal as ob- 
served by our party is the Upper Sonoran of the high arid 
plateau and lower slopes of the foothills of the Pine Forest 
Mountains, northern Humboldt County, Nevada. 
