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. Coalcomán. This specimen was reported by Peters (1954:34), who found it beneath a rock at the mouth of a heavily wooded ravine near Coalcomán at an elevation of 950 meters. The only other known specimen is from Comala, Colima, a village, like Coalcomán, that is located near the upper limits of the arid scrub forest. ~Natrix valida isabelleae~ Conant _Natrix valida isabelleae_ Conant, Nat. Hist. Misc., 126:7, September 15, 1953.--Pie de la Cuesta, Laguna Coyuca, Guerrero, México. Coahuayana; Playa Azul (2); Punto San Juan de Lima.