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 Potosí). 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.