_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 Coues Rice Rat _Oryzomys aquaticus_ Allen, Bull. Amer. Mus. Nat. Hist., 3:289, June 30, 1891. (Type from Brownsville, Cameron County, Texas.) _Oryzomys couesi aquaticus_ Goldman, N. Amer. Fauna, 43:39, September 23, 1918. _Specimens examined_, 2 as follows: 36 km. N and 10 km. W Ciudad Victoria, 1 km. E El Barretal, on Rio Purificacion, 1; 70 km. [by highway] S Ciudad Victoria and 6 km. W of the [Pan-American] highway [at El Carrizo], 1. _Remarks._--The specimens, all immatures, are slightly darker than topotypes of _O. c. aquaticus_, seemingly tending toward the darker _O. c. peragrus_ Merriam to the southward. These records of occurrence extend the known range of this subspecies approximately 210 miles to the southward and increase the possibility of continuous distribution between _O. c. aquaticus_ and _O. c. peragrus_. The male obtained south of Ciudad Victoria was taken on January 12, by William J. Shaldach, Jr., 200 yards within the tunnel of a mine at an elevation of approximately 2600 feet. This was in the Sierra Gorda, which is a part of the Sierra Madre Oriental. ~Oryzomys rostratus rostratus~ Merriam Rice Rat _Oryzomys rostratus_ Merriam, Proc. Washington Acad. Sci., 3:293, July 26, 1901. (Type from Metlaltoyuca, Pueblo, Mexico.) _Specimen examined_, 1 from 70 km. [by highway] S Ciudad Victoria and 2 km. W El Carrizo.