68 The American Naturalist. [January, ; 
` inside of hams, belly, vent and feet uniform yellowish white to the a 
bases of hairs; line of demarcation between colors of upper and lower ~ 
parts well defined ; hinder soles, heel and lower outer part of hind leg 
dusky ; ears large, minutely and scantily haired on both sides ; whisk- } 
ers black and nearly twice as long as head. 4 
Measurements (from well stuffed skin).—Total length 460; tail ver- 
tebra 216; hind foot 43; ear, from crown 25. Skull, (occipital and 
pterygoid region missing).— Length from tip of nasals to posterior end i 
of interparietal 50; base of incisor to post-palatal notch 24; greatest < 
anterior width of pterygoid fossa 2.5; distance from post-palatal noteh 
to posterior notch of incisive foramina 10.4; alveolar length of upper — 
molar series 9; greatest zygomatic breadth 27.5; interorbital con- " 
striction 6; length of nasals 20; length of mandible, (condyle to ante. 
rior point of ramus), 30; width of mandible, (tip of coronoid process to , 
angle), 15.6. A 
The closest ally of monochroura is fuscipes, from which it is distin- T 
guished by its larger size, pure yellowish white feet and underparts, its 
longer unicolor tail and dark brown upper parts. a 
Its cranial differences from fuscipes are well marked for the genus — 
They consist in the greater size, greater relative breadth, flat, less con- | : 
vex contour of cranium viewed laterally, greater relative width of | 
molars and the relative narrowness of the pterygoid fossa. a 
In monochroura the ratio of inter-parietal length to breadth is as six a 
to fourteen, in fuscipes it is as six to ten; in the former the length of 
the palatal region from post-palatal notch to incisive foramina is 11 
mm, in the latter it averagesabout 8mm. In fuscipes the post-palatal 
notch reaches beyond the middle of the last upper molar and the inci- 
sive foramina reach back opposite crowns of first upper molars; in 
monochroura the post-palatal notch is opposite the posterior cusp of last 
molar and the incisive foramina do not reach to the ante-basal line of 
the upper premolars by 1:5 mm. 
The chief differences of dentition may be seen in the upper molar. 
The coronoid process of fuscipes is flattened horizontally above and 
directed backward, in monochroura it is more erect and rounded. 
. Three specimens of this rat were taken by Mr. Kenzer, who says 
they often build a very large and conspicuous nest in the sparsely 
-Wooded foothills of the Rogue River and Siskyou Mountains. When 
driven from these nests they betake themselves to the nearest trees i 
the agility of a squirrel. N. cinerea occidentalis was not found in 
same region. 
