_Type._--Adult female, skull and skin; No. 39806, University
of Kansas, Museum of Natural History; 4 mi. W Mazamitla,
6600 ft., Jalisco, Mexico; October 18, 1950; obtained by J.
R. Alcorn, original number 12835.

_Distribution._--Known only from the Sierra del Tigre, and
probably occurs only at higher elevations within the
geographic limits of this isolated range of mountains.

_Diagnosis._--Size medium for genus (see measurements); tail
naked, short relative to length of head and body; hind foot
short; hairs of upper parts and underparts Plumbeous basally
and Orange-Cinnamon apically (capitalized color terms after
Ridgway, Color Standards and Color Nomenclature, Washington,
D. C., 1912); large nasal patch Cinnamon-Buff in two
specimens, but Pale Pinkish-Buff in holotype; white throat
spot small and inconspicuous, throat mostly bright
Cinnamon-Buff; auricular patch pure Plumbeous, hairs lacking
cinnamon-colored tips; tarsi with Cinnamon-Buff hairs;
dentition as in _P. bulleri_ except that enamel plate of
posterior wall of M1 reduced to a vestige present only on
inner fourth, outer three-fourths of posterior wall of M1
without trace of enamel; zygomata slender, bowed outward;
jugal long, widely separating maxillary and squamosal arms
of zygoma; skull deep (measured from a point on the frontal
to a point on the palate directly below and between the
maxillary teeth); rostrum narrow and short; nasals broadly
truncate posteriorly, and not decurved anteriorly; narrow
across mastoid processes of squamosals; anterior palatine
foramina small and rounded in outline, not slitlike.

_Comparisons._--Compared with _Pappogeomys bulleri_, the
only other named species of the genus, _P. alcorni_ differs,
as follows: Nasal patch cinnamon or buffy instead of white;
enamel plate of posterior wall of M1 reduced to inner fourth
rather than developed completely across posterior wall of
tooth; nasals broadly truncate posteriorly instead of narrow
and emarginate; anterior palatine foramina short and round
instead of long and slitlike.

_Measurements._--The type and an adult female topotype (in
parentheses) measure, as follows: Total length, 210 (210);
length of tail, 61 (63); length of hind foot, 29 (28);
condylobasal length, 38.0 (36.9); basila