1910] Taylor.—Two New Rodents from Nevada. 293 
are relatively thicker antero-posteriorly. A tendency toward 
sharper curvature seems to exist also. The lower incisors are 
smaller both as regards leneth and breadth. The molars are 
subject to great individual variation in shape in both species. 
They are, with individual exceptions, brown in nevadensis, black 
in desertorum. 
The rostrum in nevadensis is relatively longer and more nar- 
row than in desertorum. On the other hand, the tongues of the 
premaxillaries extending back of the nasals are relatively broader 
in nevadensis. 
The hamular processes of the pterygoid bones are straighter 
in the Nevada wood rat, and although the skulls of desertorum 
are larger, the hamulars in the latter are closer together. 
Every skull of nevadensis at hand has the bay in the dorsal 
contour of the foramen magnum emphasized. In desertorwm 
it is less prominent, and in one specimen (no. 6967) no trace of 
it 1s observable. 
The presphenoid bar separating the spheno-palatine vacuities 
is wider in all our specimens of nevadensis than in desertorwm 
except in one skull (no. 8280) in which it is so narrow as to 
approach desertorum. 
The mandible is less massive. The coronoid process is sharper 
and the outline of the cut-out portion, or bay, on the posterior 
surface is a more even curve than that of desertorum, in which 
the curve is interrupted ventrally by a sudden straightening. 
It has already been remarked that the anterior roots of the 
zygomatic arch are more narrow than in desertorum. The same 
should be said of the posterior root. These differences are among 
the best of the cranial diagnostic characters. 
Several interesting facts come to light upon examination of 
the table of cranial measurements. It is evident that the skulls 
of the Nevada animal average smaller in almost every particular. 
The fact that nevadensis, that is, the smaller-skulled animal, 
presents the longer tooth-row is a seeming exception to this 
relation of averages. The interparietal is of different shape in 
the two species, being wider in nevadensis. The height of the 
cranium at the auditory bullae is greater in nevadensis, mdi- 
cating that the bullae are more swollen in that form. 
