In Michoacán _Thamnophis dorsalis cyclides_ has been collected in a variety of habitats on the Mexican Plateau: pine-oak forest, fir forest, marshes, and cleared land from 1550 to 2800 meters. In the Sierra de Coalcomán one was taken in broad-leafed forest at 950 meters, three in pine-oak forest at 2100 meters, and one in pine forest at 2300 meters. ~Thamnophis dorsalis postremus~ Smith _Thamnophis eques postremus_ Smith, Zoologica, 27:109, October 23, 1942.--El Sabino, Michoacán, México. _Thamnophis cyrtopsis postremus_ Smith, Copeia, no. 2:140, June 8, 1951. _Thamnophis cyrtopsis cyclides_ (part), Milstead, Texas Jour. Sci., 5:368, September, 1953. _Thamnophis dorsalis postremus_, Fitch and Milstead, Copeia, no. 1:112, March 17, 1961. Apatzingán (31); Capirio (2); Charapendo; Cuatro Caminos (22); El Sabino; Lombardia (9); Nueva Italia (8); Uruapan (3). The reasons for recognizing the population of _Thamnophis dorsalis_ in the Tepalcatepec Valley as distinct from that on the surrounding highlands are presented in the discussion of _Thamnophis dorsalis cyclides_. In certain features of coloration and in the low numbers of ventrals and caudals, _T. dorsalis postremus_ shows more resemblance to _T. dorsalis sumichrasti_ than to _T. dorsalis cyclides_. According to Milstead (1953:367), _T. dorsalis cyclides_ ranges southward from the Río Balsas in southwestern México. If specimens could be obtained from the upper Balsas Basin they might show that _T. dorsalis postremus_ inhabits that extensive basin. In the Tepalcatepec Valley _T. dorsalis postremus_ is most frequently found at night in the rainy season, at which time the snakes are abundant near temporary pools where frogs are breeding. The absence of specimens from the coastal lowlands of Guerrero, Michoacán, and Colima indicate that, although the species inhabits the lowlands of the Tepalcatepec Valley, its range does not include the coastal lowlands. A female (UMMZ 119402 from Cuatro Caminos) having 139 ventrals and a body length of 576 mm., on June 20, 1958, gave birth to 25 young, of which 18 (9 males and 9 females) were preserved. In body length the males varied from 132 to 141 (137.3) mm.; the females, 125 to 137 (133.1) mm. In tail length the males varied from 38 to 44 (42.4) mm.; females, 35 to 42 (39.7) mm. The males have 138 to 147 (142.2) ventrals and 70 to 75 (72.9) caudals; females have 131 to 140 (135.8) ventrals and 63 to 71 (67.0) caudals. ~Thamnophis eques eques~ (Reuss) _Coluber eques_ Reuss, Zool. Misc., p. 152, 1834.--México. Type locality restricted to Guadalajara, Jalisco, México, by Smith and Taylor (1950a:334). _Thamnophis macrostemma macrostemma_, Smith and Taylor, Bull. U. S. Natl. Mus., 187:163, October 5, 1945. _Thamnophis subcarinata subcarinata_, Smith, Herpetologica, 5:63, May 31, 1949.