_Remarks._--Taylor (1940:393) found frogs of this species in plants along small spring-fed rivulets in an open meadow at El Chico Parque Nacional. Also, he noted that active frogs dove into the streams and took refuge in the mud on the bottom. Rabb and Mosimann (1955:1) found this species along banks of tiny streams in open meadows and noted that the frogs sought refuge in the water. At El Chico Parque Nacional on June 8, 1960, I found _Hyla robertsorum_ under rocks along small rivulets by day; at night, when the temperature was 14° C., frogs were sitting on rocks and in junipers overhanging a small stream. At the same locality on June 23 and 24, 1962, frogs of this species were found on rainy nights, when the temperature varied from 10 to 12° C. At this time the frogs were sitting on the grassy banks of rivulets in the meadow. During the day _Hyla robertsorum_ was found on the earthen banks of the rivulets in places where dense growths of grass overhung the streams. On December 23, 1959, one specimen of _Hyla robertsorum_ was found beneath a rock in a small stream in pine forest at 3.3 kilometers north of Zacualtipán. Rabb and Mosimann (1955:1) obtained tadpoles of _Hyla robertsorum_ from quiet pools of a stream at El Chico Parque Nacional. I found tadpoles in pools in rocky streams in pine forest at 3.3 kilometers north and at 8.5 kilometers southeast of Zacualtipán. Four completely metamorphosed juveniles obtained on June 8, 1960, at El Chico Parque Nacional have snout-vent lengths of 30.6 to 32.0 mm. Gravid females were found at the same locality on June 8, 1960, and June 23, 1962. [Illustration: FIG. 4. Map showing locality records for _Hyla crassa_, _Hyla pachyderma_, and _Hyla robertsorum_.] _Distribution.--Hyla robertsorum_ inhabits streams in the pine and fir forests in the higher parts (2250 to 3050 meters) of the Sierra Madre Oriental in extreme northern Puebla and eastern Hidalgo (Fig. 4). Specimens examined.--HIDALGO: 16 km. W Agua Blanca, UMMZ 106432 (6); El Chico Parque Nacional, CNHM 75786, 100124, KU 57650-71, 59824-5 (skeletons), 59914-5 (skeletons), 71269-95, 71757 (skeleton), UIMNH 10349-64, 27022-35, 39434-49, UMMZ 92462, 106401 (5), 106443 (tadpoles), USNM 114762-85, 134268; 3.3 km. N Zacualtipán, KU 53810, 60078 (tadpoles); 8.5 km. SE Zacualtipán, KU 60079 (tadpoles). PUEBLA: Honey, UMMZ 95245. #Hyla pachyderma# Taylor _Hyla pachyderma_ Taylor, Univ. Kansas Sci. Bull., 28:308-310, pl. 27, figs. 1-4, November 12, 1942 [Holotype.--USNM 115029 from Pan de Olla, Veracruz, south of Tezuitlán, Puebla, México; Hobart M. Smith collector]. Taylor and Smith, Proc. U. S. Natl. Mus., 95:588, June 30, 1945. Smith and Taylor, Bull. U. S. Natl. Mus., 194:86, June 17, 1948; Univ. Kansas Sci. Bull, 33:350, March 20, 1950. Rabb and Mosimann, Occ. Papers Mus. Zool. Univ. Michigan, 563:7-8, March 29, 1955.