_Distribution in Tamaulipas._--Probably most of northern part of state; presently known only from three localities. The two specimens examined from the Sierra de Tamaulipas were taken in a mist net in which _Eptesicus fuscus_, _Myotis keenii_, and _Tadarida brasiliensis_ also were captured. Both are females, one of which was lactating (June 20). Specimens from San Fernando probably were taken in houses by natives, who brought the bats to the collectors (Clifton and Bodley). The maxillary tooth-row and tibia are shorter, breadth across M3 narrower, and ear slightly longer in Tamaulipan specimens than in those for which measurements were given by Miller and Allen (1928:95), but the Tamaulipan specimens do not differ otherwise. The color in general is slightly more brownish than in Texan _incautus_, but about as in Oklahoman specimens examined. Three from San Fernando, Tamaulipas, are darker than others from that state. The average weight of 12 non-pregnant females from San Fernando was 11.0 (9.5-13) grams. The only male obtained at the same locality weighed 12 grams. _Measurements._--Six females from San Fernando afford the following measurements: 100.0 (95-107); 42.5 (38-46); 10.3 (10-11); 15.3 (14.5-16); length of tibia, 17.4 (16.5-18.9); length of forearm, 44.8 (43.4-45.7); greatest length of skull, 16.5 (16.1-16.9); condylobasal length, 15.6 (15.3-15.8); least interorbital constriction, 4.0 (3.9-4.1); mastoid breadth, 8.3 (8.1-8.6); length of maxillary tooth-row, 6.5 (6.3-6.7); breadth across M3, 6.5 (6.0-6.9). _Records of occurrence._--Specimens examined, 15: San Fernando, 180 ft., 13; Sierra de Tamaulipas, 10 mi. W, 2 mi. S Piedra, 1200 ft., 2. Additional record: Soto la Marina (Miller and Allen, 1928:93). =Myotis keenii auriculus= Baker and Stains Keen's Myotis 1955. _Myotis evotis auriculus_ Baker and Stains, Univ. Kansas Publ., Mus. Nat. Hist., 9:83, December 10, type from 10 m. W, 2 mi. S Piedra, 1200 ft., Sierra de Tamaulipas, Tamaulipas. 1960. _Myotis keenii auriculus_, Findley, Jour. Mamm., 41:18, February. _Distribution in Tamaulipas._--Known only from type locality (2 specimens), but probably widely distributed in western part of state. The two specimens known from Tamaulipas were caught in a mist net stretched across a narrow, brush-bordered arroyo in the Sierra de Tamaulipas. I tentatively follow Findley (1960) in arranging _auriculus_ as a subspecies of _M. keenii_. _Records of occurrence._--Specimens examined, the holotype and one topotype. =Myotis californicus mexicanus= (Saussure) California Myotis