Cerro Tancítaro (36); Opopeo; Pátzcuaro. This small rattlesnake inhabits rocky areas in pine and pine-oak forests above 1600 meters in the Cordillera Volcánica; it has been collected at 3270 meters on Cerro Tancítaro. 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 Tancítaro, but only _Crotalus pusillus_ inhabits the coniferous forests of the Sierra de Coalcomán. Klauber (1952:30) stated that despite the proximity of _Crotalus triseriatus triseriatus_ and _Crotalus triseriatus aquilus_ in Michoacán, 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 México, probably will be of great significance in understanding dispersal and differentiation of animals during the Pleistocene. SPECIES OF QUESTIONABLE OCCURRENCE Some species for which there are no authentic records from Michoacán can be expected there on zoogeographic probability. Other species have been recorded from Michoacán, but these records are doubtful for any one of several reasons. Fifteen species of such questionable occurrence are discussed below: ~Syrrhophus modestus modestus~ Taylor _Syrrhophus modestus_ Taylor, Univ. Kansas Sci. Bull., 28:304, May 15, 1942.--Hacienda Paso del Río, Colima, México. _Syrrhophus modestus modestus_, Duellman, Occ. Pap. Mus. Zool. Univ. Michigan, 594:5, June 6, 1958. This small terrestrial frog is not uncommon on the coastal lowlands and foothills in Nayarit and in Colima, where it has been collected within a few kilometers of the Michoacán border. At Tecolapa, Colima, on August 9, 1956, _Syrrhophus modestus modestus_ was found with _Tomodactylus nitidus orarius_, _Bufo marinus_, _Bufo marmoreus_, _Hyla baudini_, _Hyla smithi_, and _Phyllomedusa dacnicolor_, all of which occur on the coastal lowlands of Michoacán. Because of its solitary and secretive habits, _Syrrhophus modestus modestus_ is not common in collections. Additional field work on the coast of Michoacán should reveal the presence of the species there. ~Hyla microcephala sartori~ Smith _Hyla microcephala sartori_ Smith, Herpetologica, 7:186, December 31, 1951.--1 mi. N of Organos, S of El Triente, Guerrero, México.