of skull, posterior
margin straight or with slight median posterior angle;
incisive foramina tapered toward both ends, sometimes narrower
anteriorly than posteriorly; anterior palatal spine usually
forming a blade thickened on ventral edge, and right and left
sides usually incompletely fused; nasal septum with a
posterior notch separating vomer from maxillary; posterior
margin of palate usually bearing single or double point,
sometimes straight; interpterygoid fossa moderately wide,
lateral margins concave; sphenopalatine vacuities large;
auditory bullae of medium size; basioccipital with low median
ridge or crest; upper incisors wide, yellow or yellow-orange;
molars large, M1 wider than M2; maxillary tooth-rows long,
nearly parallel; anterointernal fold of M1 deep, cutting more
than half way across first enamel loop.

[Illustration: FIGS. 1-6. Skulls of _Neotoma mexicana_. All x 1.

FIGS. 1-2. _Neotoma mexicana scopulorum_, holotype.

FIGS. 3-6. _Neotoma mexicana fallax_, 1-1/2 mi. NW Golden, 6200 ft.,
Jefferson County, Colorado, 8 June 1948, [Male] No. 29182 KU.]

Adult in worn pelage taken in May at Two Buttes peak: no molt
in evidence; pelage thinner and rougher than in adults of same
tooth wear taken in February in unworn pelage (described
above); upper parts duller, less heavily overlaid with black;
sides less richly yellowish, slightly more pinkish in hue;
underparts with no fur white to base (as usual for the
species). The skull of this rat has narrower nasals than other
adults from Two Buttes and a longer interparietal with a
posterior median angle.

Subadult taken in April at Regnier: completing postjuvenal
(first) molt; new pelage fairly long and thick everywhere
except on neck and upper back, where covered by remaining
juvenal pelage; upper parts of new pelage duller than in
adults, sides less buffy, more grayish; juvenal pelage grayer
than new pelage; new pelage indistinguishable from same pelage
(second pelage of first year) of _N. m. fallax_.

_Comparisons._--_N. m. scopulorum_ is extremely variable in
color but averages lighter and richer in color than _N. m.
fallax_, and about the same as _N. m. inopinata_. _N. m.
scopulorum_ can be separated from either by the following
cranial differences: skull larger, more strongly arc