or
expansion of the rostrum, _P. ochraventer_ seems to be related to _P.
furvus_ and _P. latirostris_, a series of the latter being made
available for examination by Dr. George G. Lowery, Jr., of the Museum
of Zoology at Louisiana State University. However, the rostrum of these
two larger species is proportionately longer than the rostrum of _P.
ochraventer_. In size, coloration and most cranial features, _P.
ochraventer_ resembles _P. mexicanus_, although the absence, instead of
presence, of a supraorbital bead or ridge, the almost parallel-sided,
instead of more pointed, rostrum and the larger, instead of smaller,
interiormost loph of the first upper molar in _P. ochraventer_ are
well-marked differences. The baculum of _P. ochraventer_ is much
shorter with a proportionately heavier base and shaft than the baculum
of _P. mexicanus mexicanus_ (from Veracruz) and _P. m. saxatilis_ (from
Costa Rica). The geographic range of _Peromyscus ochraventer_ is not
known to meet that of _P. mexicanus_; the nearest place to the type
locality of _P. ochraventer_ from which _P. mexicanus_ has been taken
is at Xilitla approximately 225 kilometers to the southward in San Luis
Potosi (Dalquest, Occ. Papers Mus. Zool., Louisiana State Univ., No.
28:8, July 10, 1950).

The brown coloring on the underparts is a distinctive feature of _P.
ochraventer_; in adults this color differs in shade. In some specimens
patches of whitish hair give the tail a splotched appearance. Eleven of
the twenty-eight skulls and lower jaws examined have bone eroded away
from around the cheek-teeth exposing part of the roots. Most of the
fully adult animals have this condition. One adult female, no. 36959,
has the upper third molar on the right side missing, possibly as a
result of bone erosion.

These mice were taken in junglelike forest, in rocks and adjacent to
logs. Schaldach writes that "Their burrows go back under the large
limestone blocks, and each burrow where I caught a mouse has a pile of
excavated earth, like a tiny gopher mound." The trapping area was at an
elevation of approximately 2800 feet on the steep sides of a small hill
on top of which the field camp was situated. Schaldach indicated that
this locality was transitional between arid tropical and humid tropical
conditions. On January 13, 1950, a female taken was lactating and had
five recent placental scars; another taken the same day also had five
placental scars.

_Measurements._--Aver