_Hypsiboas crassus_, Cope, Bull. U. S. Natl. Mus., 32:14, 1887. _Hyla robustofemora_ Taylor, Univ. Kansas Sci. Bull., 26:389-393, figs. 3-4, November 27, 1940 [Holotype.--UIMNH 25050 (formerly EHT-HMS 16314) from Cerro San Felipe, 15 kilometers northeast of Oaxaca, Oaxaca, México; Edward H. Taylor collector]; Univ. Kansas Sci. Bull., 28:310, November 15, 1942. Smith and Taylor, Bull. U. S. Natl. Mus., 194:86, June 17, 1948. Taylor, Amer. Mus. Novitates, 1437:20, December 7, 1949. Smith and Taylor, Univ. Kansas Sci. Bull., 33:339, March 20, 1950. Rabb and Mosimann, Occas. Papers Mus. Zool. Univ. Michigan, 563:7, March 29, 1955. _Plectrohyla crassa_, Hartweg, Occas. Papers Mus. Zool. Univ. Michigan, 437:1, June 30, 1941. Stuart, Occas. Papers Mus. Zool. Univ. Michigan, 455:6, January 5, 1942. _Diagnosis._--Maximum snout-vent length in males 54 mm.; snout in dorsal profile round; tarsal fold strong; inner metatarsal tubercle small and elliptical; outer metatarsal tubercle small, flat, and indistinct; foot fully webbed; nuptial spines on thumb small; thoracic fold absent; anal opening at level of middle of femur; dorsum dull olive-green; belly creamy yellow; chin gray with yellow flecks; flanks dull olive-green with scattered cream-colored spots; and stripe faint, cream-color; vocal slits absent. _Description._--The following description is based on UIMNH 25050 from Cerro San Felipe, Oaxaca. Adult male having a snout-vent length of 53.7 mm.; tibia length, 26.9 mm., 50.1 per cent of snout-vent length; foot length (measured from proximal edge of inner metatarsal tubercle to tip of longest toe), 25.4 mm.; greatest width of head, 17.6 mm., 32.8 per cent of snout-vent length; head length, 16.0 mm., 29.8 per cent of snout-vent length; diameter of eye, 5.4 mm.; diameter of tympanum, 1.5 mm., 27.8 per cent of diameter of eye. Snout short, in lateral profile bluntly rounded, in dorsal profile broadly round; canthus absent; loreal region nearly flat; lips thick and not flaring; nostrils barely protuberant; internarial distance, 3.8 mm.; interorbital distance, 4.7 mm., somewhat broader than width of eyelid, 3.8 mm. Heavy dermal fold from posterior corner of eye above tympanum and then to insertion of forearm; tympanum concealed above, its diameter about equal to its distance from eye. Forearm thick; distinct fold on wrist; prepollex enlarged bearing patch of small nuptial spines continuous on side of digit; similar patch on second finger; subarticular tubercles small and round, none bifid; few supernumerary tubercles on proximal segments of digits; large, flat palmar tubercle; fingers long and slender; length of fingers from shortest to longest, 1-2-4-3; discs moderately large; rudimentary web between second and third fingers and between third and fourth. Legs thick; heels overlap by about one-fourth length of shank when hindlimbs adpressed;