Transverse bars are present on the shanks in _Hyla staufferi_ from Costa Rica northward to México, whereas in Panamá all the individuals have a longitudinal stripe on the shank (Table 7, Pl. 2). The interorbital spot or bar is more noticeable in northern populations than in specimens from Panamá. Frogs from Costa Rica and northward have the toes about three fourths webbed, whereas in Panamá the toes are about two fifths webbed. The mating calls of the northern and Panamanian populations are similar, but the notes have a longer duration in the northern populations and a higher dominant frequency in Panamanian populations. _Hyla staufferi_ is the most variable member of the _Hyla rubra_ group in Central America. The Panamanian populations are geographically separated from the Costa Rican and more northern populations by an area of tropical rainforest in the Golfo Dulce region in southeastern Costa Rica and adjacent Panamá. _Hyla staufferi_ does not occur on the Caribbean versant of Costa Rica and Panamá. The Golfo Dulce region and the Caribbean versant are humid and inhabited by _Hyla elaeochroa_. _Hyla staufferi_ is an inhabitant of subhumid and xeric areas. On the basis of the discontinuous variation in several characters which correlate with the disjunct distribution of the two populations, two subspecies of _Hyla staufferi_ are recognized. The accounts that follow apply equally to each. _Cranial Osteology._--The skull of _Hyla staufferi_ is flat and longer than wide. The premaxillary is small and bears 9 to 13 teeth (mean for 5 specimens, 11.3). The alary process of the premaxillary is small, concave posteriorly and vertical. Ventrally, the premaxillary is united to the prevomers by partially ossified cartilage. The maxillary is slender and usually bears 49 to 70 teeth (mean for 5 specimens, 60.7). The pars facialis of the maxillary is convex and less than twice the height of the pars dentalis. The nasal is large, rounded anteriorly, and pointed posteriorly in dorsal view. The nasal comprises about 40 per cent of the total length of the skull. Anteromedially the two nasals converge; posteriorly they overlap the sphenethmoid. The nasals lack a concavity in the midlateral surface. Dorsally, the sphenethmoid is wider than long, roughly pentagonal in shape; the frontoparietal is elongate, narrow, and smooth, with a small supraorbital process anteriorly. The frontoparietal fontanelle is narrow anteriorly and wide posteriorly. TABLE 7.--Geographic Variation in Size and Color in Males of _Hyla staufferi_. (Means in parentheses below observed ranges.)