Milstead (1953) had available few specimens of _Thamnophis dorsalis_ from the Tepalcatepec Valley. The large series now in existence shows that the population in the Tepalcatepec Valley differs distinctly from that inhabiting the Mexican Plateau, Cordillera Volcánica, and Sierra de Coalcomán. Therefore the name _T. dorsalis postremus_ Smith (1942) is resurrected for the population in the Tepalcatepec Valley. _T. dorsalis cyclides_ and _T. dorsalis postremus_ differ in color pattern (Fig. 10) and in scutellation (Table 6). Specimens from the Mexican Plateau and mountain ranges have a distinct light stripe on the second and third scale rows, a dark brown dorsum having squarish black spots, and a row of dark spots on the first row of dorsal scales. Specimens from the Tepalcatepec Valley have a grayish brown dorsum having smaller and less distinct dark spots and no light stripe on the second and third scale rows; the first, second, and third rows of scales are colored like the venter. In some specimens there are small dark flecks on the first row of dorsal scales. TABLE 6.--VARIATION IN SCUTELLATION IN THAMNOPHIS DORSALIS. +---------------------------------+-------+---------+------------+ | Character |Mexican|Sierra de|Tepalcatepec| | |Plateau|Coalcomán| Valley | +------------------+--------------+-------+---------+------------+ | Ventrals | Female N | 31 | 2 | 32 | | | Mean | 164.0 | 156.5 | 144.6 | | | Range|153-171| 154-159 | 138-151 | | +--------------+-------+---------+------------+ | | Male N | 19 | 2 | 32 | | | Mean | 153.5 | 154.7 | 138.3 | | | Range|149-159| 149-159 | 131-141 | +------------------+--------------+-------+---------+------------+ | Caudals | Female N | 28 | 2 | 29 | | | Mean | 83.8 | 81.0 | 73.4 | | | Range|80-100 | 79-83 | 70-79 | | +--------------+-------+---------+------------+ | | Male N | 14 | 2 | 28 | | | Mean | 78.0 | 72.0 | 68.5 | | | Range| 71-87 | 72 | 63-73 | +------------------+--------------+-------+---------+------------+ One specimen from Uruapan (1550 meters) and one from Coalcomán (950 meters) are intermediate in color pattern between _T. dorsalis cyclides_ and _T. dorsalis postremus_. Both have indistinct lateral stripes and only small dark spots below the stripes. In scutellation these specimens are like _T. dorsalis cyclides_.