Comparisons.—Ptychohyla euthysanota macrotympanum can be distinguished from both P. spinipollex and P. leonhardschultzei by the absence of bold black and white marbling on the flanks, as well as by the characters given in the diagnosis; furthermore, from the former it differs in having more and smaller horny nuptial tuberosities and from the latter by having the snout, in lateral profile, rounded above instead of angulate. Ptychohyla euthysanota macrotympanum differs from P. e. euthysanota by normally having a paler dorsum, narrower stripe on upper lip, and no distinct lateral stripe.
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 Río 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 Río Grijalva and Río 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 Río Grijalva and Río Cuilco.
Specimens examined.—Mexico: Chiapas: 6 km. NE of Chiapa de Corzo, TCWC 16183; 16 km. E of Chiapa de Corzo, AMNH 62141; Linda Vista, 2 km. NW of Pueblo Nuevo Solistahuacán, KU 58049-51, 59939 (skeleton); Río Hondo, 9.5 km. S of Pueblo Nuevo Solistahuacán, KU 58047-8, 60046-7, 60048-9 (tadpoles); San Fernando, MZTG 15, 17; Tonina (ruins), KU 41592.
Guatemala: Huehuetenango: Jacaltenango, UMMZ 123139 (tadpoles); 0.5 km. E of Jacaltenango, UMMZ 123142-3; 2 km. S of Jacaltenango, UMMZ 123141; 2 km. W of San Pedro Necta, UMMZ 123140 (tadpoles).