_Description and variation._--No noticeable geographic variation is apparent in either structural features or coloration in this species. All specimens lack a dorsolateral dark stripe and white line, although a dark line is present on the canthus and dissipates in the loreal region. A broad interorbital brown bar is present in all specimens. The color pattern on the dorsum invariably consists of a broad, dark, chevron-shaped mark in the scapular region and a broad dark chevron or transverse bar in the sacral region. The shanks invariably have two or three dark brown transverse bars. When active at night individuals are yellowish tan above with chocolate brown markings (Pl. 14). The belly is white, and the thighs are pale yellowish tan. The iris is dark bronze-color. In breeding males the vocal sac is yellow. By day some individuals were observed to change to creamy gray with distinct darker markings. _Remarks._--Although tadpoles of this species have not been found, observations on the breeding sites indicate that the tadpoles probably develop in ponds. Except for calling males observed around a pool in a stream-bed 11.8 kilometers west-northwest of Tierra Colorada, Guerrero, all breeding congregations have been found at temporary ponds. Smith (1951:186) named _Hyla sartori_ as a subspecies of _Hyla microcephala_. This subspecific relationship seemed reasonable until analysis of the mating calls showed that the call of _H. sartori_ is more nearly like that of _H. phlebodes_ than that of _H. microcephala_. The broad hiatus separating the ranges of _H. microcephala_ and _H. sartori_ is additional evidence for considering _H. sartori_ as a distinct species. [Illustration: Fig. 4. Map showing locality records for _Hyla sartori_.] _Distribution._--_Hyla sartori_ occurs in mesophytic forests to elevations of about 300 meters on the Pacific slopes of southern México from southwestern Jalisco to south-central Oaxaca (Fig. 4). The lack of specimens from Colima and Michoacán probably reflects inadequate collecting instead of the absence of the species there. On the basis of available habitat the species would be expected to occur in Nayarit, but extensive collecting there has failed to reveal its presence. The semi-arid Plains of Tehuantepec apparently limit the distribution to the east.