Part 4

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

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 Río Purificacíon, 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.

Remarks.--This immature male is paler than specimens of O. r. rostratus from the state of Veracruz. This locality extends the known range of this species northward a distance of approximately 100 miles. Previously it had been recorded from only as far north as Alta Mira, Tamaulipas (Goldman, N. Amer. Fauna, 43:54, September 23, 1918). This specimen was trapped on February 16 in a rodent runway in dense grass in a fallow cane field.

~Oryzomys fulvescens engraciae~ Osgood

Fulvous Rice Rat

Oryzomys fulvescens engraciae Osgood, Jour. Mamm., 26:300, November 14, 1945. (Type from Hacienda Santa Engracia, northwest of Ciudad Victoria, Tamaulipas, Mexico.)

Specimens examined, 5 from 70 km. [by highway] S Ciudad Victoria and 2 km. E El Carrizo.

Remarks.--These specimens are referred to O. f. engraciae on the basis of their pale color and narrow interorbital space. They were taken in runways in dense grass in fallow cane fields.

~Sigmodon hispidus toltecus~ (Saussure)

Hispid Cotton Rat

Sigmodon hispidus toltecus Bailey, Proc. Biol. Soc. Washington, 15:110, June 2, 1902.

Specimens examined, 23 as follows: 36 km. N and 10 km. W Ciudad Victoria, 1 km. E El Barretal, on Río Purificacíon, 1; 70 km. [by highway] S Ciudad Victoria and 2 km. W El Carrizo, 22.

Remarks.--Among named kinds of Sigmodon this series most closely approaches S. h. toltecus to the southward. The specimens are slightly lighter in color of the upper parts than are examples of this same subspecies from 8 km. NW of Potrero, Veracruz, but in other ways are similar. The single specimen from 36 km. N and 10 km. W Ciudad Victoria is a skull only, but seems closest to S. h. toltecus. As is often the case with collections of Sigmodon, this series contains mostly immatures.

Cotton rats were found abundantly in cultivated areas. Local farmers stated that these rats were destructive to sugar cane by girdling the stems one and one-half inches above the ground.

~Neotoma micropus micropus~ Baird