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. 1911. _Liomys irroratus alleni_, Goldman, N. Amer. Fauna, 34:56, September 7. _Distribution in Tamaulipas._--Extreme southwestern part of state.