In the Tepalcatepec Valley _T. dorsalis postremus_ is most frequently found at night in the rainy season, at which time the snakes are abundant near temporary pools where frogs are breeding. The absence of specimens from the coastal lowlands of Guerrero, Michoacan, and Colima indicate that, although the species inhabits the lowlands of the Tepalcatepec Valley, its range does not include the coastal lowlands.
A female (UMMZ 119402 from Cuatro Caminos) having 139 ventrals and a body length of 576 mm., on June 20, 1958, gave birth to 25 young, of which 18 (9 males and 9 females) were preserved. In body length the males varied from 132 to 141 (137.3) mm.; the females, 125 to 137 (133.1) mm. In tail length the males varied from 38 to 44 (42.4) mm.; females, 35 to 42 (39.7) mm. The males have 138 to 147 (142.2) ventrals and 70 to 75 (72.9) caudals; females have 131 to 140 (135.8) ventrals and 63 to 71 (67.0) caudals.
~Thamnophis eques eques~ (Reuss)
_Coluber eques_ Reuss, Zool. Misc., p. 152, 1834.--Mexico.
Type locality restricted to Guadalajara, Jalisco, Mexico, by Smith and Taylor (1950a:334).
_Thamnophis macrostemma macrostemma_, Smith and Taylor, Bull. U. S. Natl. Mus., 187:163, October 5, 1945.
_Thamnophis subcarinata subcarinata_, Smith, Herpetologica, 5:63, May 31, 1949.
_Thamnophis eques eques_, Smith, Copeia, no. 2:139, June 8, 1951.
Jiquilpan; Lago de Cuitzeo; Lago de Patzcuaro (17); Patzcuaro (5); Tangancicuaro; Tupataro (2); Undameo; Zacapu.
Although this snake has been collected in open pine-oak forest and in oak-bunch gra.s.s a.s.sociations, it seems to reach its greatest abundance in marshes on the Mexican Plateau at elevations of 1550 to 2300 meters.
~Thamnophis melanogaster canescens~ Smith
_Thamnophis melanogaster canescens_ Smith, Zoologica, 27:117, October 23, 1942.--Chapala, Jalisco, Mexico.
Lago de Cuitzeo (5); Lago de Patzcuaro; Patzcuaro; Tacicuaro; Tangamandapio (2).
This species of garter snake seems to be most abundant in the marshes adjacent to the lakes on the Mexican Plateau in Michoacan and Jalisco.
At these elevations (1550 to 2200 meters) it often is found in a.s.sociation with _Thamnophis eques eques_ and sometimes with _Thamnophis dorsalis cyclides_. On June 11, 1958, individuals of this species were found in a hyacinth-choked marsh at Tangamandapio at night.
One specimen from Tangamandapio (UMMZ 119414) had, in life, a dark chocolate brown dorsum, reddish brown sides, and cream-colored belly, chin, and l.a.b.i.als. There were no longitudinal dorsal stripes.
~Thamnophis scalaris scaliger~ (Jan)
_Tropidonotus scaliger_ Jan, Elenco sistematico degli Ofidi, p. 70, 1863.--No type locality designated. Type locality restricted to Mexico City, Distrito Federal, by Smith and Taylor (1950a:329).
_Thamnophis scalaris scaliger_, Smith, Zoologica, 27:103, October 23, 1942.
Cerro Tancitaro (2); Nahuatzen; Opopeo; 26 km. S of Patzcuaro.
The few specimens of this species from Michoacan have been collected at elevations from 1800 to 3400 meters in pine or fir forest in the Cordillera Volcanica.
~Micrurus distans michoacanensis~ (Duges)
_Elaps diastema michoacanensis_ Duges, La Naturaleza, ser.
2, 1:487, 1891.--Michoacan. Type locality restricted to Apatzingan, Michoacan, Mexico, by Smith and Taylor (1950a:335).
_Micrurus distans michoacanensis_, Zweifel, Amer. Mus.
Novitates, 1953:11, June 26, 1959.
Apatzingan (6).
All specimens were collected in the arid scrub forest of the Tepalcatepec Valley. The number of black rings on the body varies from six to eleven. In this respect they agree with the diagnosis of this subspecies presented by Zweifel (1959b:9).
~Micrurus laticollaris~ (Peters)
_Elaps marcgravii laticollaris_ Peters, Monats. Akad. Wiss.
Berlin, p. 877, 1869.--Izucar de Matamoros, Puebla, Mexico.
_Micrurus laticollaris_, Schmidt, Publ. Field Mus. Nat.
Hist., zool. ser., 20:39, December 11, 1933.
El Sabino (2); Lombardia.
This species ranges throughout the Balsas-Tepalcatepec Basin westward into Colima; specimens from Michoacan were collected in arid scrub forest at elevations from 500 to 1050 meters. The limited observations on _Micrurus distans michoacanensis_ and _M. laticollaris_ indicate that, at least in the Tepalcatepec Valley, _M. laticollaris_ seems to inhabit slightly more mesic areas than does _M. distans michoacanensis_.
~Pelamis platurus~ (Linnaeus)
_Anguis platura_ Linnaeus, Systema naturae, ed. 12, 1:391, 1766.--Pine Island, Pacific Ocean.
_Pelamis platurus_, Gray, Ann. Philos., p. 15, 1825.
Boca de Apiza.
In November, 1955, Alfonzo Gonzales, a geographer from the University of Texas, observed sea snakes on the beaches of Michoacan. In May, 1956, Donald D. Brand of the University of Texas gave me one specimen of _Pelamis platurus_ that he obtained on March 2, 1956, at Boca de Apiza.
Furthermore, he supplied me with the following observations based on his field work along the coast of Michoacan from the Rio Coahuayana to Maruata from March 1, to April 15, 1956. At that time many sea snakes were observed; in some places living and dead individuals were seen on the beaches; innumerable snakes were seen in the surf. When live individuals were taken from the beach and thrown into the ocean, they usually swam to sh.o.r.e. Many partially eaten individuals were seen protruding from crab holes. Inquiries among the natives resulted in the following information: Sea snakes are frequently seen between November and April, but most commonly in March and April, at which time the water is cold. The natives referred to the sea snakes as "culebra del mar."
Most natives said that the snakes were not poisonous; others did not know of any venomous properties. In May, 1956, I worked the coastal region from the Rio Coahuayana to La Placita and saw no sea snakes. In the summer of 1950 James A. Peters, and in the summer of 1951 I worked nearly the entire coastal region of Michoacan; during that time no _Pelamis_ were seen. Insofar as I know, this is the first report of such seasonal activity in _Pelamis platurus_ in the Americas.
~Agkistrodon bilineatus bilineatus~ Gunther
_Ancisdrodon bilineatus_ Gunther, Ann. Mag. Nat. Hist., ser.
3, 12:364, 1863.--Pacific coast of Guatemala.
_Agkistrodon bilineatus bilineatus_, Burger and Robertson, Univ. Kansas Sci. Bull., 34 (1):213, October 1, 1951.
Apatzingan; El Sabino; La Playa; Los Reyes.
All specimens from Michoacan are from inland localities between 300 and 1500 meters. The one from Los Reyes (USNM 46416) was collected by Nelson and Goldman on February 13, 1903. The elevation of Los Reyes (1500 meters) seems unusually high for this species, but otherwise there is no reason to doubt the authenticity of the record. Goldman (1951:192) in his description of Los Reyes stated: "Los Reyes is near the boundary between the Lower Austral and Arid Upper Tropical Zones but is preponderantly tropical in zonal character. The regular crops are mainly sugar cane, rice, and corn." Thus the biotic features of the area are not noticeably different from those at El Sabino and La Playa at lower elevations. The development of extensive agriculture through irrigation in the Tepalcatepec Valley and planting of rice and sugar-cane in that area may produce a more widespread habitat for this snake.
The absence of specimens from the coastal lowlands is due solely to inadequate collecting; the natives there know the snake and report that it is not uncommon in certain areas.
~Crotalus basiliscus basiliscus~ (Cope)
_Caudisonia basilisca_ Cope, Proc. Acad. Nat. Sci.