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.