This species, as is known, is active by day and by night. It occurs mainly in grassy areas and most of the specimens examined were trapped there. But, one mile east of La Pesca, specimens were taken on a beach having sparse grass. _Neotoma micropus_ and _Spermophilus spilosoma_, but no smaller rodents, were taken there. Also, many crabs were found in the traps. Possibly only the relatively large rodents are able to compete successfully with the crabs. The specimen from one kilometer east of El Barretal was caught in a rat-trap set in front of small hole in a fence of dead brush that surrounded a cornfield. The area outside the fence supported mesquite and ebony trees (10-12 feet high) and the ground was covered with cat claw. Six miles north and six miles west of Altamira, the two young specimens were taken on a small grassy island surrounded by mud. According to natives, _Sigmodon_ injures corn and sugar cane. Probably other species of rodents are responsible for some or all of such damage since other kinds of rodents were taken in the same areas. Dice (1937:245) reported females from the Sierra San Carlos that carried 8 embryos of 18 mm., 5 × 33, 7 embryos very small, and 8 × 20. Females were collected on July 22, 29, and 30. =Sigmodon hispidus berlandieri= Baird 1855. _Sigmodon berlandieri_ Baird, Proc. Acad. Nat. Sci. Philadelphia, 7:333, type from Río Nazas, Coahuila. 1902. _Sigmodon hispidus berlandieri_, V. Bailey, Proc. Biol. Soc. Washington, 15:106, June 2. _Distribution in Tamaulipas._--From Jaumave and Llera to north. This subspecies is distinguished from _S. h. toltecus_ by larger size and paler, grayish coloration. TABLE 3.--DATA ON REPRODUCTION. =========================+=============+=========+============= LOCALITY | Date | Embryos | Size in mm. -------------------------+-------------+---------+------------- 4 mi. N La Pesca | May 26 | 4 | 30 Sierra de Tamaulipas | June 10 | 3 | 10 Sierra de Tamaulipas | June 11 | 4 | 10 Sierra de Tamaulipas | June 20 | 2 | 20 Ciudad Victoria | July 12 | 5 | 5 Jaumave | July 28 | 4 | 14 Jaumave | July 29 | 6 | 25 San Fernando | August 30 | 7 | 20 San Fernando | August 31 | 8 | 11 Vicinity of Nuevo Laredo | November 15 | 3 | 5 Vicinity of Nuevo Laredo | November 16 | 5 | 2 -------------------------+-------------+---------+-------------