_Smilisca puma_ dispersed northward onto the Caribbean lowlands of southern Nicaragua. Its southward movements probably were limited by the ridges of the Talamanca Range that extend to the Caribbean coast in the area of Punta Cahuita in Costa Rica. _Smilisca sila_ dispersed along the Pacific lowlands and slopes of the mountains from eastern Costa Rica and western Panamá through eastern Panamá to northern Colombia. Climatic fluctuation in the Pleistocene evidently provided sufficient altitudinal shifts in environments in the Talamanca Range to permit _S. sordida_ to move onto the Pacific slopes. From its upland distribution the species followed streams down to both the Caribbean and Pacific lowlands, where it is sympatric with _S. puma_ on the Caribbean lowlands and _S. sila_ on the Pacific lowlands.
The evolution of the species-groups of _Smilisca_ was effected through isolation by physical barriers in the Cenozoic; the differentiation of the species was initiated by further isolation of populations by changes in physiography and climate. Present patterns of distribution resulted from Pleistocene and post-Wisconsin climatic changes. Today, sympatric species have different breeding habits and breeding calls which reinforce the differences in morphology.
The genus _Smilisca_ is composed of six species of tree frogs; each species is defined on the basis of adult morphology, larval characters, and breeding behavior. Keys are provided to aid in the identification of adults and of tadpoles.
Analysis of the characters and examination of type specimens indicates that several currently-recognized taxa are synonymous, as follows:
1. _Hyla beltrani_ Taylor, 1942 = _Smilisca baudini_. 2. _Hyla gabbi_ Cope, 1876 = _Smilisca sordida_. 3. _Hyla manisorum_ Taylor, 1954 = _Smilisca baudini_. 4. _Hyla nigripes_ Cope, 1876 = _Smilisca sordida_. 5. _Hyla wellmanorum_ Taylor, 1952 = _Smilisca puma_.
_Smilisca phaeota cyanosticta_ Smith, 1953 is elevated to specific rank, and one new species, _Smilisca sila_, is named and described.
The skeletal system of developmental stages and the adult of _Smilisca baudini_ is described, and the skull is compared with that of other members of the genus.