_Ptychohyla euthysanota macrotympanum_ occurs sympatrically with _Plectrohyla guatemalensis_ and _P. matudai matudai_. Each of the last two has a bony prepollex, rather rugose skin on the dorsum, and more squat body. Other sympatric species are _Hyla walkeri_, which has a green dorsum with brown markings and a rather pointed snout, and _Hyla sumichrasti_, a small yellow frog usually lacking vomerine teeth. _Life History._--This species breeds in clear mountain streams in mixed pine and broad-leafed forest. Males call from trees and bushes along the streams. The breeding call consists of a soft "wraack," repeated three to nine times with intervals of 2.7 to 3.4 seconds between notes. Each note has a duration of 0.60 to 0.65 second, and a rate of 92 to 100 pulses per second; the dominant frequency falls between 3000 and 3200 cycles per second (Pl. 11B). The call is indistinguishable from that of _P. e. euthysanota_. Tadpoles in various stages of development were found in the Rio Hondo, Chiapas, on June 16, 1960. The smallest tadpole has a total length of 24.1 mm.; in this individual the sixth lower tooth row has barely started to develop. A metamorphosing frog taken at the same time has a snout-vent length of 19.8 mm., a short remnant of the tail, and the mouth and tongue developed, whereas another individual having a snout-vent length of 17.8 mm. and a tail 31.0 mm. in length still has larval teeth. Three completely metamorphosed juveniles collected by L. C. Stuart at Jacaltenango, Guatemala, on June 6 and 7, 1955, have snout-vent lengths of 16.0, 16.0, and 16.1 mm. _Remarks._--Tanner (1957:52) based the description of _Hyla macrotympanum_ on a single female, which, of course, lacked the characters diagnostic of _Ptychohyla_. On the basis of general external characters Tanner suggested that _Hyla macrotympanum_ was related to _H. miotympanum_, from which it differed in having a larger tympanum and a bifid subarticular tubercle beneath the fourth finger. The collection of additional females, together with males of the species, has shown that _Hyla macrotympanum_ is a _Ptychohyla_. Intergradation between _Ptychohyla euthysanota_ and _P. macrotympanum_ has not been demonstrated. Currently their ranges are separated by the dry valleys of the Rio Grijalva and Rio Cuilco. The similarity in structure of the adults and tadpoles and the indistinguishable breeding calls are the basis for considering the two populations subspecies. _Distribution._--This species occurs in mixed pine and broad-leafed forests at elevations of 700 to 1700 meters on the southern slopes of the Chiapan Highlands and Sierra de Cuchumatanes, in Guatemala. These forests are on the south facing slopes north of the valleys of the Rio Grijalva and Rio Cuilco.