Proceedings of the United States National Museum . romyscus difficilis (Osgood, 1909, p. 179).The range of the other form, P. townsendii, is in part inhabits the lower elevations of the arid plateau and desert rangesof north-central Mexico north of the transverse volcanic belt, andthe arid valleys of Jahsco, Morelos, and Oaxaca south of the trans-verse volcanic belt. In addition, it occurs together with P. mexicanusin the southern extremity of the Sierra Madre Occidental (Sierra deValparaiso, 8,200 feet) and in the transverse volcanic belt (SantaRosa, 9,500 feet, Convento de A
Proceedings of the United States National Museum . romyscus difficilis (Osgood, 1909, p. 179).The range of the other form, P. townsendii, is in part inhabits the lower elevations of the arid plateau and desert rangesof north-central Mexico north of the transverse volcanic belt, andthe arid valleys of Jahsco, Morelos, and Oaxaca south of the trans-verse volcanic belt. In addition, it occurs together with P. mexicanusin the southern extremity of the Sierra Madre Occidental (Sierra deValparaiso, 8,200 feet) and in the transverse volcanic belt (SantaRosa, 9,500 feet, Convento de Acolman, and Lago Texcoco, 7,500feet. However, it should be noted that the latter locahties are rela-tively arid, despite their high elevation (Davis, 1944, p. 371; Gold-man, 1951, p. 146). This pattern of distribution might exist without intergradationbetween the two forms if they were: (1) Subspecies with seasonalmigrations; (2) ecologically isolated subspecies; or (3) distinct,partially sympatric, species. 146 PROCEEDINGS OF THE NATIONAL MUSEUM. Figure 18.—Sympatiy of Plecotus mexicanus (triangular symbols) and Plecotus tozvnsendii(circular symbols) in Mexico. Seasonal movement is not apparent in available samples (table 5).P. mexicanus is found in northern and southern parts of its range inboth winter and summer. P. tomisendii has been taken at high eleva-tions in the transverse volcanic belt (in the range of P. mexicanus)in both summer and winter, has been found south of the belt in sprmg,late summer, and fall, and north of the belt at all seasons. The theory of conspecificity becomes less tenable when of one or the other of the subspecies cannot be demon-strated. The phenomenon of overlapping ends of a chain of sub- AMERICAN BATS—HANDLEY 147 Table 5.—Seasonal distribution of P. mexicanus and P. townsendii in Mexico, asdetermined from specimens for which collection date is known P. mexicanus North of transverse volcanic belt In transverse volcanic be
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