prepollex much enlarged with patch of small nuptial spines continuous on side of digit; similar line of nuptial spines on inner edge of second finger; subarticular tubercles round, moderate in size, none bifid; supernumerary tubercles small and present only proximally; fingers long and slender; length of fingers from shortest to longest, 1-2-4-3; discs moderately large, that on third finger about size of tympanum; no web between first and second fingers; rudimentary web between other fingers. Legs robust; heels over-lap by about one-fourth length of shank when hind limbs adpressed; tibiotarsal articulation extending to posterior corner of eye; tarsal fold weak, extending to about middle of tarsus; inner metatarsal tubercle moderately large, flat, and elliptical; outer metatarsal tubercle small, round, and indistinct; subarticular tubercles round; supernumerary tubercles small, in single row on proximal segments of each digit; toes moderately long and slender; length of toes from shortest to longest, 1-2-5-3-4, the fifth nearly as long as third; toes nearly fully webbed; web extending to base of penultimate phalanx of fourth toe and to discs on other toes; discs small, about two-thirds size of those on fingers. Anal opening above middle of thighs; anal sheath short, deeply creased medially; heavy transverse dermal fold above anus; no large anal tubercles. Skin of all dorsal surfaces, chin, and ventral surfaces of limbs, except proximal parts of thighs, smooth; belly and proximal parts of thighs areolate; thoracic fold present, weak. Tongue elliptical, slightly longer than wide, not notched behind, and free posteriorly for about one-fourth of its length; vomerine teeth 3-3, situated on small, widely separated, transverse ridges between rather small elliptical inner nares; no vocal slits.

Color (in alcohol) dark brown with irregular darker reticulations on dorsal surfaces of head, body, and limbs; flanks brown with small creamy white spots; posterior surfaces of thighs dark brown; chin creamy tan; belly grayish brown with cream-colored flecks; ventral surfaces of limbs pale brown; webbing on feet gray; small white spots in anal region.

Color (in life) chocolate brown with darker brown reticulations and irregular blotches above; flanks brown with yellow spots; belly gray to grayish brown with faint cream-colored spots; iris a deep bronze color.

Variation.—In males the total number of vomerine teeth varies from 4 to 7. In many specimens the vomerine ridges are larger and more closely approximated medially than in the specimen described above. Females attain snout-vent lengths of 51 mm., have as many as 9 vomerine teeth, and have a proportionately larger tympanum than males. Some of the largest specimens of both sexes have indistinct cream-colored pustules scattered on the ventral surface of the forearm. Some individuals have nearly uniform grayish brown ventral surfaces; in others the chin, as well as the abdomen, is brown with cream-colored spots. The dorsal surfaces of some specimens are nearly uniform dark brown with no reticulations. In others the dorsum is paler brown with distinct darker mottling; in some of these there is little mottling laterally, so that there is the effect of an irregular, pale brown, dorsolateral stripe.

Tadpoles.—The tadpoles of this species were described by Rabb and Mosimann (1955). Tadpoles obtained from streams at 3.3 kilometers north and at 8.5 kilometers southeast of Zacualtipán, Hidalgo, are like those described by Rabb and Mosimann in having ⅔ tooth rows, peglike serrations on the beaks, and long rounded tails. The largest tadpole (KU 60078) has small hind legs, a body length of 22 mm., and a total length of 61 mm.

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.

Fig. 4. Map showing locality records for Hyla crassa, Hyla pachyderma, and Hyla robertsorum.

Hyla pachyderma Taylor