Specimens examined are tentatively assigned to Dipodomys merriami atronasus. They differ from typical atronasus as pointed out by Lidicker (1960:177). He noted that individuals from the eastern edge of the range of D. m. atronasus were slightly paler than typical specimens, but I found Tamaulipan material to be much darker, especially behind the nose and ears (blackish instead of brownish), than specimens from Aguascalientes, San Luis Potosí and Zacatecas.
Specimens examined were collected under the same conditions and in the same areas as D. ordii durranti. The average weight of 20 adults (11 females and nine males) was 46.6 (38-50) grams.
Records of occurrences.—Specimens examined, 27: Nicolás, 56 km. NW Tula, 5500 ft., 16; Tajada, 23 mi. NW Tula, 5200 ft., 4; 15 mi. N Tula, 1; 8 mi. N Tula, 4500 ft., 3; 9 mi. SW Tula, 3900 ft., 3.
Additional record: Tula (Lidicker, 1960:178).
Liomys irroratus
Mexican Spiny Pocket Mouse
This species is probably the most common rodent in Tamaulipas. It was taken at almost every locality sampled and was associated with many other kinds of rodents. Its distribution is state-wide with the exception of the extreme northwestern part. Two subspecies are represented in Tamaulipas, L. i. alleni, which occurs in the western side of the Sierra Madre Oriental in the southwest part of the state, and L. i. texensis, which occupies the rest of the range of the species in the state.
At Soto la Marina specimens were taken in dense brush, around the cultivated fields; no burrows were seen and all specimens were trapped before 10:00 p.m. On the Sierra de Tamaulipas, Liomys was collected in practically all microhabitats. In the vicinity of San Fernando, individuals were trapped in a dry area in which vegetation consisted of mesquite, cactus and chollas; the ground there was covered with dry leaves and small sticks, and burrows were found near the base of the mesquite bushes. One specimen was taken near the house of a woodrat. Two kilometers west of El Carrizo, where Liomys irroratus is called "ratón tuza," specimens were collected on rocks inclined at an angle of about twenty-five degrees that were covered with zacatón grass and some bushes. Some individuals were taken in a sugar cane field that was surrounded by bushes and tall grass; Baiomys taylori, Sigmodon hispidus, and Peromyscus leucopus were taken in the line of traps. One specimen was caught in a trap baited with banana.
Some dates concerning reproduction of Liomys irroratus in Tamaulipas are as follows: La Pesca, May 25, one female lactating and one female pregnant with 4 embryos that measured 8 mm.; Jaumave, July 26-29, three females lactating and three pregnant females that carried 6 embryos (6 mm.), 6 embryos (15 mm.), and 5 embryos (15 mm.); Palmillas, July 23, a female with 1 embryo measuring 6 mm.; Nicolás, October 19, a female carrying 4 embryos measuring 3 mm.
Liomys irroratus alleni (Coues)
1881. Heteromys alleni Coues, Bull. Mus. Comp. Zool., 8:187, March, type from Río Verde, San Luis Potosí.