The known distributions of _N. micropus_ and _N. angustapalata_ do not overlap (neither does the distribution of _N. albigula_ overlap with either in Tamaulipas). The four specimens of _N. micropus_ having the deep re-entrant angle in M1 are from localities near where the ranges of _angustapalata_ and _micropus_ probably meet. This could be interpreted in two ways: (1) these four specimens can be regarded as intergrades between _angustapalata_ and _micropus_, in which case the former species should be placed as a subspecies of the latter. Or the four specimens, which were collected along with other specimens that lack deep re-entrant angles in the M1, can be assigned, on the basis of the deep angle, to _angustapalata_, in which case the species _micropus_ and _angustapalata_ would be in part sympatric. Until more material from critical areas is available for study, I continue to recognize _angustapalata_ as a monotypic species. I agree with Hooper that it is closely related to _N. micropus_. _Measurements._--A female (58865) from 8 km. west and 10 km. north of El Encino, measured as follows: 404; 198; 41; 32; greatest length of skull, 49.7; basilar length, 40.8; zygomatic breadth, 25.9; length of nasals, 18.8; length of incisive foramina, 10.8; length of maxillary tooth-row, 9.9; greatest breadth of interpterygoid space, 4.0. _Records of occurrence._--Specimens examined, 3: 8 km. W, 10 km. N El Encino, 400 ft., 1; type locality, 2. =Neotoma micropus= Southern Plains Wood Rat Most of the specimens examined were trapped in brushy areas. On the Sierra de Tamaulipas, wood rats were caught in steel traps set near or between rocks. In the vicinity of La Pesca, specimens were trapped on the beach where _Spermophilus spilosoma_ and _Sigmodon hispidus_ were taken also. Two females, obtained on May 19 and June 10 at Soto la Marina and on the Sierra de Tamaulipas, respectively, each carried 2 embryos that were 40 mm. in crown-rump length. Dice (1937:254) reported that two females collected on July 24 and August 16 on the Sierra San Carlos each carried 2 embryos that ranged from 34 to 36 mm. in crown-rump length. _Neotoma micropus_ occurs throughout the Tamaulipan Biotic Province and is represented in Tamaulipas by two subspecies, each of which has its type locality in the state. Intergradation between the two takes place at Soto la Marina. =Neotoma micropus littoralis= Goldman 1905. _Neotoma micropus littoralis_ Goldman, Proc. Biol. Soc. Washington, 18:31, February 2, type from Altamira, 100 ft., Tamaulipas. _Distribution in Tamaulipas._--From the Sierra de Tamaulipas southward. Weight of two males and three non-pregnant females was 248, 254, 185, 210, 240 grams, respectively. _Records of occurrence._--Specimens examined, 14: Sierra de Tamaulipas, 2 mi. S, 10 mi. W Piedra, 1200 ft., 6; 6 mi. N, 6 mi. W Altamira, 8.