Variation.—Adult males have snout-vent lengths from 35.3 to 44.4 mm., and adult females from 43.4 to 50.9 mm. No notable variation in structure is displayed in the type series. In some individuals the dark reticulation on the dorsum is faint. Juveniles in life had dorsal colorations varying from rich brown with darker reticulations to pale green or gray with dark green reticulations. Some adults when collected were pale green with faint or no dorsal reticulations; later these individuals darkened. In all specimens the anal stripe is absent, and the flanks are heavily spotted.
Comparisons.—Hyla charadricola differs from all other members of the Hyla bistincta group in the following combination of characters: truncate snout, green dorsum, and absence of a thoracic fold. From other hylids that occur in the same area, Hyla charadricola differs from Hyla miotympanum and H. arborescandens, both of which are green dorsally, by having a truncate snout and longer fingers with less webbing. Hyla eximia, though green, has brown dorsal spots, shorter fingers, and a round snout. Hyla robertsorum differs in having a round snout and brown dorsum, and Hyla taeniopus is much larger, has transverse bands on the limbs, and has extensive webbing between fingers.
Remarks.—At the type locality, a shallow rocky stream in pine forest, Hyla charadricola was found beneath rocks at the edge of fast moving sections of the stream and beneath rocks in shallow riffles in the stream. Most of the frogs were in water. At night they were found sitting on rocks in the stream. Hyla miotympanum, which is abundant at the type locality, lives in bushes and beneath rocks along the stream but usually is not found in the riffles inhabited by Hyla charadricola. At Lago de Tejocotal Hyla charadricola was found beneath rocks near the shore of the lake and by a stream in the pine forest. Individuals were found on low vegetation over-hanging a small stream in pine-oak forest four kilometers southwest of Tianguistengo.
Five recently metamorphosed young (KU 58424-9) found at the type locality on June 8, 1960, have snout-vent lengths of 22.4 to 24.0 (average 23.2) mm. The young are colored like the adults, except that in life the dorsum is a brighter green and the flanks are more yellow than tan and have less dark spotting than in adults.
Distribution.—Hyla charadricola inhabits streams in pine and pine-oak forests at elevations of 2000 to 2300 meters in northern Puebla and eastern Hidalgo (Fig. 2).
Specimens examined.—Hidalgo: Lago de Tejocotal, 11 km. E Acaxochitlán, KU 58438, UMMZ 104032, 118165; 4 km. SW Tianguistengo, KU 53811-2. Puebla: 11.7 km. W Huachinango, UMMZ 121567 (5); Río Totolapa, 14.4 km. W Huachinango, KU 53813-5, 55624, 58414-37, 59813 (skeleton), 59886 (skeleton), MCZ 34964-5, UIMNH 50966, UMMZ 118166 (5), S-2242 (skeleton).
Hyla robertsorum Taylor, Univ. Kansas Sci. Bull., 26:393-396, figs. 5-6, November 27, 1940 [Holotype.—CNHM 100124 (formerly EHT-HMS 16264) from El Chico Parque Nacional, Hidalgo, México; Mr. and Mrs. Radclyffe Roberts and Edward H. Taylor collectors]; Univ. Kansas Sci. Bull., 28:310, November 15, 1942. Taylor and Smith, Proc. U. S. Natl. Mus., 95:589, June 30, 1945. Smith and Taylor, Bull. U. S. Natl. Mus., 194:87, June 17, 1948; Univ. Kansas Sci. Bull., 33:333, March 20, 1950. Rabb and Mosimann, Occas. Papers Mus. Zool. Univ. Michigan, 563:1-9, March 29, 1955. Duellman, Univ. Kansas Publ. Mus. Nat. Hist., 15:48, December 20, 1961.
Diagnosis.—Maximum snout-vent length in males, 48 mm.; snout in dorsal profile rounded; tarsal fold short and weak; inner metatarsal tubercle moderate in size and elliptical; outer metatarsal tubercle small, round, and indistinct; webbing extending to base of penultimate phalanx of fourth toe; nuptial spines on thumb small; weak thoracic fold present; anal opening above level of middle of thighs; dorsum dark brown with dark reticulations; venter brown with cream-colored flecks; flanks brown with creamy white spots; anal stripe absent; small white spots in anal region; vocal slits absent.