292 University of California Publications in Zoology. [Vou-5 
the ratio of the tail vertebrae to the total length is greater in 
desertorum, due to the same cause. 
Another form whose range may be supposed to be contiguous 
is Neotoma lepida (Thomas, Ann. Mag. Nat. Hist., 6th series, 
XII, Sept., 1893, p. 235). The type locality of this species is 
Williams Spring, just south of Champlin Mts., Juab County, 
Utah. Although no specimens of this form are at hand, a study 
of the original description seems to show that nevadensis is 
distinct. 
The ears of lepida are described as being large, their minute 
hairs whitish. In the Nevada wood rat these hairs are gray or 
brown. In some of the specimens there is a tendeney for the 
hairs on the inner side of the pinna to be light gray, tipped with 
blaek. Those on the outside are very dark brown, almost black. 
Quoting from Thomas’ deseription of lepida (1. c.): ‘*Tail 
very thickly haired, so much so as to be intermediate between 
that of the round-tailed and the bushy-tailed species, the scales 
entirely hidden by the hairs; its color mixed brownish fawn 
> 
above, white below.’’ The tails of our examples of nevadensis 
are rather thinly haired, the scales being hidden by the hairs in 
two of our specimens only (nos. 8281, 7888). Nor can our speci-. 
mens be said to be intermediate between the round-tailed and the 
bushy-tailed species. Other shght differences appear to exist, 
showing that lepida must be a.different form. 
CRANIAL CHARACTERS.—The skulls of nevadensis average 
smaller than those of desertorum, and are differently shaped. 
(See table of cranial measurements.) The frontal profile is not 
flattened on the same plane. By placing the skull on a hori- 
zontal flat surface with the basicranial face downward, and set- 
ting the edge of a ruler on the flat part of the frontal, the plane 
of flattening is shown to be tipped a little downward anteriorly. 
In desertorum the plane is nearly horizontal, or tipped slightly 
downward posteriorly. Thus the highest part of the skull when 
in this position is formed by the temporal region instead of the 
frontal bones. Both this difference and the other distinctive 
cranial characters may be more readily apprehended by the in- 
spection of the appended plates. 
The upper incisors are not only narrower and shorter but 
