The Amphibians and Reptiles of Michoacan, Mexico Part 24

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 gra.s.sland 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), who found it beneath a rock at the mouth of a heavily wooded ravine near Coalcoman at an elevation of 950 meters. The only other known specimen is from Comala, Colima, a village, like Coalcoman, 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, Mexico.

Coahuayana; Playa Azul (2); Punto San Juan de Lima.

Three females and one male have, respectively, 133, 135, 135, and 131 ventrals, and 68, 68, 73, and 75 caudals. The grayish stippling on the posterior ventral surfaces mentioned by Conant (1953:9) is not visible on these specimens. In the small individuals from Punto San Juan de Lima and from Coahuayana there are four longitudinal rows of dark spots on the dorsum; in two large females from Playa Azul the spots are barely discernible.

All of the specimens from Michoacan were found in the coastal lowlands; those from Playa Azul were collected from a small brackish, mangrove-lined lagoon.

~Storeria storerioides~ (Cope)

_Tropidoclonium storerioides_ Cope, Proc. Acad. Nat. Sci.

Philadelphia, 17:190, December 26, 1865.--Mexican Plateau.

Type locality restricted to Tres c.u.mbres, Morelos, Mexico, by Smith and Taylor (1950a:336).

_Storeria storerioides_, Garman, Mem. Mus. Comp. Zool., 8(3):29, June, 1883.

Dos Aguas (11); Puerto de Garnica; Tancitaro (11); Tzitzio; Uruapan; 16 km. NW of Zacapu.

Three males and six females from the Sierra de Coalcoman have, respectively, 122-128 (125.3) and 126-136 (130.0) ventrals, and 46-47 (46.7) and 38-42 (39.1) caudals. Four males and eleven females from the Cordillera Volcanica have, respectively, 124-132 (128.5) and 127-139 (136.4) ventrals, and 43-48 (44.7) and 38-44 (40.2) caudals. These data show that, although there is little difference in the number of caudals, specimens from the Sierra de Coalcoman have fewer ventrals than do specimens from the Cordillera Volcanica. Of eleven specimens from the Sierra de Coalcoman, two have black bellies. Five others from the Sierra de Coalcoman and one from Puerto de Garnica in the Cordillera Volcanica have the bellies heavily stippled with black, giving a gray appearance.

Melanistic tendencies in this species have been discussed by Anderson (1960:64), who examined the specimen from Tzitzio. In life, one specimen from Dos Aguas (UMMZ 119451) had a cream-colored belly; the edges of the ventrals were dark brick-red.

In Michoacan this snake inhabits pine-oak, pine, and fir forests at elevations between 1550 and 2800 meters in the Cordillera Volcanica and the Sierra de Coalcoman. Most specimens were found beneath rocks; the one from Tzitzio was removed from the stomach of a Mexican Motmot (Anderson, 1960:66).

~Thamnophis dorsalis cyclides~ Cope

_Thamnophis cyrtopsis cyclides_ Cope, Proc. Acad. Nat. Sci.

Philadelphia, 13:299, December 28, 1861.--Cape San Lucas, Baja California (in error). Type locality restricted to Guanajuato, Guanajuato, Mexico, by Smith and Taylor (1950a:330). Smith, Copeia, no. 2:140, June 8, 1951.

Milstead, Texas Jour. Sci., 5:368, September, 1953.

_Thamnophis eques eques_ (_nec._ Reuss), Smith, Zoologica, 27:106, October 23, 1942. Bogert and Oliver, Bull. Amer.

Mus. Nat. Hist., 83:356, March 30, 1945.

_Thamnophis vicinus_ Smith, Zoologica, 27:104, October 23, 1942.--Temazcal, Michoacan, Mexico.

_Thamnophis dorsalis cyclides_, Fitch and Milstead, Copeia, no. 1:112, March 17, 1961.

Barolosa; Coalcoman; Dos Aguas (3); Los Reyes; Morelia (16); Opopeo; Pino Gordo; Tacicuaro (16); Tancitaro (14); Tangamandapio (2); Temazcal (2); Tzintzuntzan; Uruapan.

The snakes comprising the former _Thamnophis eques_-group have undergone extensive taxonomic and nomenclatural shuffling by Smith (1942 and 1951), Bogert and Oliver (1945), Milstead (1953), and Fitch and Milstead (1961). Smith recognized in Michoacan three members of the _T. eques_ (= _dorsalis_) complex: _eques eques_, _eques postremus_, and _vicinus_.

Later, Smith (1951) showed that the specific name _eques_ had been misapplied, so that _T. eques eques_ became _T. cyrtopsis cyclides_, and _T. eques postremus_ became _T. cyrtopsis postremus_; under this arrangement _T. vicinus_ stood unchanged. In the meantime, Bogert and Oliver (1945:359) presented a reinterpretation of Smith's data and suggested that _T. vicinus_, which differs from _T. dorsalis cyclides_ only in lacking a middorsal stripe, "... is not a species, but only a pattern phase, possibly a simple mutant of _T. e. eques_" (= _T.

dorsalis cyclides_, by present arrangement). Milstead (1953) agreed with Bogert and Oliver on the status of _T. vicinus_; furthermore, on the basis of only a few specimens, Milstead concluded that _T. cyrtopsis postremus_ was not subspecifically distinct from _T. cyrtopsis cyclides_. Recently, Fitch and Milstead (1961) showed that _Thamnophis dorsalis_ Baird and Girard (1853) was the correct name for the snakes that had been recognized as _Thamnophis cyrtopsis_ Kennicott (1860).

Consequently, the snakes referred to _T. eques eques_ by Smith (1942) and to _T. cyrtopsis cyclides_ by Smith (1951) and Milstead (1953) are now _T. dorsalis cyclides_.

Aside from one specimen from Temazcal and nine from Morelia (paratypes of _T. vicinus_), only two other specimens completely lacking the middorsal stripe have been seen; one is a male (UMMZ 102510) having 161 ventrals and an incomplete tail from Pino Gordo, and the other is a male (CNHM 39060) from Tancitaro having 158 ventrals and an incomplete tail.

A female from Tancitaro (CNHM 39061) having 153 ventrals and 77 caudals has no lateral stripes and only a narrow middorsal stripe on the anterior part of the body. Throughout the region where _T. vicinus_-like snakes have been found, typical _T. dorsalis cyclides_ occurs in much greater numbers. I concur with Bogert and Oliver in placing _T. vicinus_ as a synonym of _T. dorsalis cyclides_.

[Ill.u.s.tration: FIG. 10. Dorsal color pattern of _Thamnophis dorsalis cyclides_ (A) and _Thamnophis dorsalis postremus_ (B).]

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 Volcanica, and Sierra de Coalcoman. 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|Coalcoman| 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 Coalcoman (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_.

In Michoacan _Thamnophis dorsalis cyclides_ has been collected in a variety of habitats on the Mexican Plateau: pine-oak forest, fir forest, marshes, and cleared land from 1550 to 2800 meters. In the Sierra de Coalcoman one was taken in broad-leafed forest at 950 meters, three in pine-oak forest at 2100 meters, and one in pine forest at 2300 meters.

~Thamnophis dorsalis postremus~ Smith

_Thamnophis eques postremus_ Smith, Zoologica, 27:109, October 23, 1942.--El Sabino, Michoacan, Mexico.

_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.

Apatzingan (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 Rio Balsas in southwestern Mexico. If specimens could be obtained from the upper Balsas Basin they might show that _T. dorsalis postremus_ inhabits that extensive basin.