_Type._--Female, adult, skin and skull; no. 36958, Univ.
Kansas Mus. Nat. Hist.; 70 km. [by highway] S Ciudad
Victoria and 6 km. W of the [Pan-American] highway [at El
Carrizo], Tamaulipas, Mexico; 12 January 1950; obtained by
William J. Schaldach, Jr., original no. 566.
_Range._--Known only from the type locality; probably found
in other localities along the humid, east face of the Sierra
Madre Oriental in Tamaulipas.
_Diagnosis._--Size medium (see measurements); upper parts
near Ochraceous Tawny (capitalized color terms after
Ridgway, Color Standards and Color Nomenclature, Washington,
D. C., 1912), brighter on sides and duller on back; cheeks,
sides of neck, shoulders and upper forelegs lighter, between
Ochraceous Buff and Ochraceous Orange; eye ring dark;
underparts light Cinnamon Buff, breast patch brighter; ears
dusky, sparsely covered with hairs colored like back; feet
white; tail scaly in appearance, indistinctly bicolored with
short dark hairs above and short pale hairs below; skull
without beaded or ridged supraorbital border; rostrum
expanded anteriorly with sides almost parallel; teeth with
strongly developed outer accessory cusps on the first and
second upper molar teeth; anteriormost loph
(parastyle-protoconule of Goldman, N. Amer. Fauna, 43:11,
September 23, 1918) of the first upper molar large, almost
as broad as greatest breadth of tooth.
_Comparisons._--_Peromyscus ochraventer_ has been compared
with _P. difficilis_ (specimens from Veracruz), _P. boylei_
(Veracruz), _P. banderanus_ (Guerrero), _P. mexicanus_
(Veracruz), _P. furvus_ (Veracruz), and _P. latirostris_
(San Luis Potosi). From _P. difficilis_, _P. ochraventer_
differs in having underparts distinctively brownish, rostrum
expanded anteriorly with sides almost parallel, anteriormost
loph of the first upper molar larger, and auditory bulla
smaller. From _P. boylei_, _P. ochraventer_ differs in
having underparts distinctively brownish, tail less
distinctly bicolored, rostrum expanded anteriorly with sides
almost parallel, and anteriormost loph of the first upper
molar larger. From _P. banderanus_, _P. ochraventer_ differs
in having underparts distinctively brownish, tail less
distinctly bicolored, rostrum expanded anteriorly with sides
almost parallel, anteriormost loph of the first upper molar
larger, auditory bulla smaller, and in lacking a beaded or
ridged supraorbital border. From _P. mexicanus_, _P.
ochraventer_ differs in having underparts distinctively
brownish, tail not irregularly blotched with dusky, rostrum
expanded anteriorly with sides almost parallel, anteriormost
loph of the first upper molar larger, and in lacking a
beaded or ridged supraorbital border. From _P. furvus_ and
_P. latirostris_, _P. ochraventer_ differs in being smaller,
having underparts distinctively brownish, tail not
irregularly blotched with dusky, rostrum proportionately
shorter, and interpterygoid space relatively narrower.
_Remarks._--_Peromyscus ochraventer_ is considered to be a distinct
species showing little evident relationship with other Mexican
_Peromyscus_. In the shape of the skull, especially the anterior
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._--Average and extreme measurements of seven
adult males and six adult females of _P. ochraventer_ from
the type locality are, respectively, as follows: Total
length, 238.0 (227-249), 236.5 (226-248); length of tail,
124.4 (117-127), 122.2 (116-128); length of hind foot, 25.6
(24-26), 25.5 (25-26); length of ear from notch, 20.9
(20-21), 20.7 (20-21); greatest length of skull, 31.0
(30.6-31.9), 30.8 (30.5-31.0); basilar length, 23.3
(22.7-23.8), 23.4 (23.0-23.9); zygomatic breadth, 15.1
(14.6-15.7), 15.0 (14.9-15.2); post palatal length, 10.6
(10.5-10.9), 10.9 (10.5-11.2); interorbital breadth, 4.7
(4.5-4.9), 4.7 (4.6-4.8); mastoidal breadth, 12.8
(12.4-13.2), 12.8 (12.6-12.9); length of nasals, 11.6
(10.8-12.0), 11.6 (11.2-11.7); length of shelf of bony
palate, 4.7 (4.5-4.8), 4.6 (4.5-4.7); length of palatine
slits, 6.3 (6.0-6.5), 6.2 (6.0-6.4); length of diastema, 8.2
(8.0-8.5), 8.2 (8.1-8.4); alveolar length of upper
molariform tooth-row, 4.4 (4.3-4.6), 4.4 (4.3-4.5).
_Specimens examined_, 28, from the type locality.
~Oryzomys couesi aquaticus~ Allen