cia_ 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, Mexico.

Emiliano Zapata (2); between Morelia and Ciudad Hidalgo;
Tacicuaro; Tangamandapio.

Two of the specimens from Michoacan (UMMZ 118948 from Tangamandapio and
UIMNH 19138 from Tacicuaro) 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 Michoacan 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 Michoacan." They gave the range of
_Trimorphodon upsilon_ as: "Southern Chihuahua south to central
Michoacan, 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 Michoacan 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,
Mexico.

Coalcoman.

This specimen was reported by Peters (1954:34), w