Philadelphia, September 30, 1864.--Colima. Type locality restricted to Colima, Colima, Mexico, by Smith and Taylor (1950a:328).
_Crotalus basiliscus basiliscus_, Gloyd, Nat. Hist. Misc., 17:1, April 23, 1948.
Apatzingan (4); Camachines; Coalcoman; El Ticuiz.
Specimens from southern Michoacan have fewer ventrals and caudals than do those from the northern part of the range; three males and three females have, respectively, 178, 182, 182, 185, 186, and 188 ventrals, and 27, 28, 29, 22, 29, and 29 caudals. Klauber (1952:81) gave the following data for _Crotalus basiliscus_ (based on specimens from the entire range, except Oaxaca): ventrals in males, 179-201 (191.4), in females, 185-206 (197.6); caudals in males, 26-36 (30.7), in females, 21-29 (24.4). Klauber (1952:84) remarked that the one specimen that he had seen from Apatzingan had fewer ventrals and caudals than most other specimens. The low numbers of ventrals and caudals in specimens from Michoacan, as compared with more northern populations, may be indicative of a trend in the reduction of the numbers of these scutes from north to south. The southernmost examples of _Crotalus basiliscus_ (_Crotalus basiliscus oaxacus_ from Oaxaca) have 172-175 ventrals and 21 caudals (Gloyd, 1948).
In Michoacan _Crotalus basiliscus basiliscus_ has been found in arid habitats on the coast, in the Tepalcatepec Valley, and in the lower parts of the Sierra de Coalcoman. All specimens are from localities below 1070 meters in elevation.
~Crotalus durissus culminatus~ Klauber
_Crotalus durissus culminatus_ Klauber, Bull. Zool. Soc. San Diego, 26:65, August 8, 1952.--El Sabino, Michoacan, Mexico.
El Sabino (18).
These specimens are part of the type series and were collected by Hobart M. Smith near the upper limits of the arid scrub forest at an elevation of about 1050 meters on the lower slopes of the Cordillera Volcanica at the northern edge of the Tepalcatepec Valley. They were discussed in detail by Klauber (1952:66-70).
~Crotalus intermedius intermedius~ Troschel
_Crotalus intermedius_ Troschel, _in_ von Muller, Reisen in Vereiningten Staaten, Canada und Mexico, vol. 3, p. 613, 1865.--Type locality unknown.
_Crotalus intermedius intermedius_, Klauber, Bull. Zool.
Soc. San Diego, 26:9, August 8, 1952.
Cerro Tancitaro.
The one specimen is from the pine forests on the Cordillera Volcanica.
At the present time this species is known from scattered localities in west-central Veracruz, Oaxaca, Michoacan, and as _Crotalus intermedius omiltema.n.u.s_ in Central Guerrero. Apparently it is restricted to montane environments.
~Crotalus molossus nigrescens~ Gloyd
_Crotalus molossus nigrescens_ Gloyd, Occ. Pap. Mus. Zool.
Univ. Michigan, 325:2, January 28, 1936.--Four miles west of La Colorada, Zacatecas, Mexico.
Carapan; Los Conejos; Patzcuaro; Tacicuaro (5).
In Michoacan this species has been found in pine forests between 1550 and 2300 meters in the Cordillera Volcanica. I expected to find it in the Sierra de Coalcoman, but inquiries among the natives living in the pine forests of that mountain range revealed that the people there have no knowledge of a large species of rattlesnake.
~Crotalus polystictus~ (Cope)
_Caudisonia polysticta_ Cope, Proc. Acad. Nat. Sci.
Philadelphia, 17:191, December 26, 1865.--Tableland of Mexico. Type locality restricted to Tupataro, Guanajuata, Mexico, by Smith and Taylor (1950a:330).
_Crotalus polystictus_ Cope, _in_ Yarrow, Wheeler"s Rept.
Geog. Geol. Expl. Surv. W. 100th. Mer., vol. 5, p. 533, 1875.
Tacicuaro (4); Tupataro (2).
Formerly this species was abundant in the marshes around Lago de Chapala. The draining of these marshes probably resulted in reducing the numbers of these rattlesnakes. The species is known only from the Mexican Plateau at elevations of 1450 to 2400 meters.
~Crotalus pusillus~ Klauber
_Crotalus pusillus_ Klauber, Bull. Zool. Soc. San Diego, 26:34, August 8, 1952.--Tancitaro, Michoacan, Mexico.
Acuaro de las Lleguas (2); Carapan; Cerro Tancitaro (16); Dos Aguas (12).
Aside from the type series of _Crotalus pusillus_ from Cerro Tancitaro and one specimen from Carapan referred to the species by Klauber (1952:38), there are fourteen specimens from the Sierra de Coalcoman.
These specimens (UMMZ 112566-7, 118591-9, 118601, 121512-3) are like _Crotalus pusillus_ from Cerro Tancitaro in having the prefrontals paired, a black proximal rattle, and the underside of the tail black.
The prefrontals are bordered posteriorly by one scale in two specimens, by two scales in three specimens, and by three scales in the other nine.
The snakes from the Sierra de Coalcoman have 40 to 46 (42) dorsal body blotches. Ten males have 150-158 (154.4) ventrals and 29-33 (31.0) caudals; two females have 157 and 160 ventrals, and 25 and 27 caudals.
The largest specimen is a male having a body length of 545 mm. and a tail length of 63 mm. The only noticeable difference between the specimens from the Sierra de Coalcoman and the topotypic series is that the latter have fewer dorsal blotches; the range of variation is 33 to 46 (39.8).
Most specimens of this species have a grayish brown dorsum and dark brown dorsal blotches. Two specimens from Dos Aguas (UMMZ 118596 and 118599) are pale brown above and have indistinct blotches.
One specimen from Dos Aguas regurgitated a large _Gerrhonotus imbricatus imbricatus_; of two others from the same locality, one regurgitated a _Sceloporus bulleri_ and an _Eptesicus fuscus_. The latter specimen was collected at the entrance of a small cave, where it probably had captured the bat.
In the Cordillera Volcanica _Crotalus pusillus_ has been obtained in pine-oak forest at elevations between 1550 and 1800 meters. In the Sierra de Coalcoman two specimens were taken in pine forest at an elevation of 2300 meters; ten other were found beneath rocks and logs in pine-oak forest at an elevation of 2100 meters.
~Crotalus triseriatus aquilus~ Klauber
_Crotalus triseriatus aquilus_ Klauber, Bull. Zool. Soc. San Diego, 26:24, August 8, 1952.--Alvarez, San Luis Potosi, Mexico.
Morelia (10); Tacicuaro (2).
I am following Klauber (1952) in a.s.signing some of the specimens of this species from Michoacan to the subspecies _aquilus_ and others to _C. t.
triseriatus_. The distinguishing characters of these subspecies are given by Klauber (1952:28). On the basis of the few localities from which the species is known in Michoacan it seems as though _C. t.
aquilus_ inhabits the open gra.s.sy areas on the Mexican Plateau and the a.s.sociated open pine-oak or oak-bunch gra.s.s habitats to the north and east of the Cordillera Volcanica. _Crotalus triseriatus aquilus_ has been collected at elevations from 1600 to 2000 meters in Michoacan.
~Crotalus triseriatus triseriatus~ (Wagler)
_Uropsophus triseriatus_ Wagler, Naturliches System der Amphibien, p. 176, 1830.--Mexico. (Probably Mexico City.)
_Crotalus triseriatus triseriatus_, Klauber, Bull. Zool.
Soc. San Diego, 26:19, August 8, 1952.
Cerro Tancitaro (36); Opopeo; Patzcuaro.
This small rattlesnake inhabits rocky areas in pine and pine-oak forests above 1600 meters in the Cordillera Volcanica; it has been collected at 3270 meters on Cerro Tancitaro. The series reported by Schmidt and Shannon (1947:84) is a mixture of specimens of _Crotalus triseriatus_ and _Crotalus pusillus_. The two species are found together on Cerro Tancitaro, but only _Crotalus pusillus_ inhabits the coniferous forests of the Sierra de Coalcoman. Klauber (1952:30) stated that despite the proximity of _Crotalus triseriatus triseriatus_ and _Crotalus triseriatus aquilus_ in Michoacan, there is no evidence of intergradation. He went on to suggest that additional material might show that the two named populations actually are distinct species. The specimens that have been studied since Klauber"s investigations also show no evidence of intergradation, but there still is no known sympatry of the populations.
The small montane rattlesnakes belonging to the species _C. pricei_, _C.
pusillus_, and _C. triseriatus_ present a problem in systematics and distribution worthy of intensive investigation. A knowledge of the distribution and relationships of the various populations of these snakes, together with other species also living in isolated populations on the higher mountains in Mexico, probably will be of great significance in understanding dispersal and differentiation of animals during the Pleistocene.