In Michoacán this species has been collected in semi-arid habitats at elevations from 300 to 1430 meters in the Tepalcatepec Valley and lower slopes of the Cordillera Volcánica. In this area it occurs sympatrically with Trimorphodon biscutatus biscutatus.
In life, adults have a pale tan dorsal ground color and rich chocolate brown cross-bands; the eye is pale grayish tan. A juvenile from Coalcomán has black cross-bands on a pale grayish tan ground color. As stated by Schmidt and Shannon (1947:83) and Peters (1954:32), the type specimen of Trimorphodon fasciolata Smith from Cascada Tzararacua is indistinguishable from specimens of Trimorphodon latifascia.
Seven males have 209 to 223 (216.5) ventrals; one female has 227 ventrals. The number of dark cross-bands on the body varies from 12 to 16 (13.5). The relationships of this species are with Trimorphodon tau on the Mexican Plateau. In fact, additional specimens from the headwaters of the Tepalcatepec Valley and the lower slopes of the Mexican Plateau in eastern Michoacán and adjacent Jalisco may show that the two are conspecific. Trimorphodon latifascia differs from tau in having fewer dark cross-bands on the body and in lacking an interocular bar.
Trimorphodon tau Cope
Trimorphodon tau Cope, Proc. Amer. Philos. Soc., 11:151, 1869.—Quiotepec, Oaxaca, México.
Emiliano Zapata (2); between Morelia and Ciudad Hidalgo; Tacícuaro; Tangamandapio.
Two of the specimens from Michoacán (UMMZ 118948 from Tangamandapio and UIMNH 19138 from Tacícuaro) have cream-colored, Y-shaped marks on the head. These markings supposedly are characteristic of Trimorphodon upsilon. One specimen from Emiliano Zapata (UMMZ 118950) and one from between Morelia and Ciudad Hidalgo (EHT-HMS 21402) have a cream-colored line on the parietal suture; in another specimen from Emiliano Zapata (UMMZ 118949) the anterior end of this line is expanded, giving the appearance of an incipient "Y". Thus, the nature of the markings on the head in specimens from Michoacán is intermediate between the typical condition in Trimorphodon tau and the usual condition in T. upsilon. Smith and Taylor (1945:148) gave the range of Trimorphodon tau as: "Central Guerrero, in the Sierra Madre del Sur; central Oaxaca; and the edge of the plateau in central Michoacán." They gave the range of Trimorphodon upsilon as: "Southern Chihuahua south to central Michoacán, east to central Hidalgo." Specimens referable to T. tau have been found at La Joya de Salas, near Ciudad Victoria, and near Llera, Tamaulipas (see Smith and Darling, 1952:85, and Martin, 1958:74). Some of these specimens also show combinations of characteristics of T. tau and T. upsilon. Smith and Darling (loc. cit.) suggested that T. tau and T. upsilon be considered as subspecies. However, if T. tau and T. upsilon are subspecies, intergrades would be expected between the ranges of the two populations and not on the northeastern and southwestern periphery of their combined ranges. Instead, the limited evidence now available suggests that T. tau and T. upsilon are names based on a highly variable character of color pattern of the head, and that only one species is involved.
In Michoacán this species inhabits the mesquite grassland on the Mexican Plateau.
Tropidodipsas occidentala Oliver
Tropidodipsas occidentala Oliver, Occ. Pap. Mus. Zool. Univ. Michigan, 360:20, November 20, 1937.—Comala, Colima, México.