_Diagnosis._--Small frogs (Male to 26 mm., Female to 27 mm.); dorsolateral and paravertebral stripes complete; longitudinal dark gray stripe on shank; thighs unmarked; interorbital bar usually absent; toes about three fifths webbed; gray to brownish gray above. _Variation._--_Hyla staufferi altae_ is less variable in size, proportions, and color pattern than is _H. s. staufferi_. The size varies from 21.7 to 26 mm. (23.6) in 72 males. The ratio of tibia to snout-vent length is 0.42 to 0.50 (0.45), slightly less than in the northern subspecies. In color pattern 94.5 per cent of the individuals have complete dorsal stripes, and all have a longitudinal stripe on the shank (Table 7). _Distribution._--This subspecies is restricted to subhumid forests and savannas on the Pacific lowlands of Panamá. _Hyla s. altae_ is presently known to occur from Chepo in east-central Panamá through the Azuero Peninsula to Concepción, Chiriquí, in western Panamá (Fig. 7). _Specimens Examined._--Panamá: _Canal Zone_: No specific locality, TNHC 24406; 2.8 km SW Fort Kobbe, KU 101679. _Chiriquí_: 14.4 km E Concepción, AMNH 69799-801; 6.6 km N David, TNHC 32013-4; 2 km S David, AMNH 68802. _Coclé_: 1 km NE El Caño, KU 101662-75; El Valle de Antón, AMNH 59601-5, KU 77333-47; 7 km SSW Penonomé, KU 101654-61. _Los Santos_: Tonosí, KU 101246 (tadpoles), 101697-701. _Panamá_: 2 km WSW Chepo, KU 101680-8; 6 km WSW Chepo, KU 77324-27; El Cangrejo (Panamá), KU 101676-8; Nueva Gorgona, AMNH 69991, 69798; 1.5 km W Pacora, KU 77328-32; 2 km N Tocumen, KU 101689-95; 8 km NE Tocumen, KU 101696. EVOLUTIONARY HISTORY My assumptions regarding the evolutionary history of the _Hyla rubra_ group in Central America were derived partly from interpretations of the evolutionary history of other animal groups (Simpson, 1943, 1965; Dunn, 1931b; Stuart, 1950; Duellman, 1958, 1960, 1963, 1965; and Duellman and Trueb, 1966). The origin and early evolution of the group probably occurred prior to the Mid-Pliocene in the lowlands of South America, because the greatest diversity of the group is in Brazil. Differentiation into two or more subgroups took place in South America prior to the late Pliocene. At the end of the Pliocene, shortly after the closure of the Colombian Portal, many South American animals migrated into Central America (Simpson, 1943, Maldonado-Koerdell, 1964, and Savage, 1966). It is likely that the _Hyla rubra_ group entered Central America at that time; apparently two stocks (_rubra-elaeochroa-staufferi_ stock and _boulengeri-foliamorta_ stock) migrated into Central America.