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 Volcánica 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 Müller, 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 Tancítaro. The one specimen is from the pine forests on the Cordillera Volcánica. At the present time this species is known from scattered localities in west-central Veracruz, Oaxaca, Michoacán, and as _Crotalus intermedius omiltemanus_ 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, México. Carapan; Los Conejos; Pátzcuaro; Tacícuaro (5). In Michoacán this species has been found in pine forests between 1550 and 2300 meters in the Cordillera Volcánica. I expected to find it in the Sierra de Coalcomán, 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 México. Type locality restricted to Tupátaro, Guanajuata, México, 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. Tacícuaro (4); Tupátaro (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.--Tancítaro, Michoacán, México. Acuaro de las Lleguas (2); Carapan; Cerro Tancítaro (16); Dos Aguas (12).