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. The tadpoles are described, compared, and illustrated; the larval development of _Smilisca phaeota_ is described. Breeding behavior and breeding calls are described and compared. Some species of _Smilisca_ have breeding choruses. Two species, _S. sila_ and _sordida_, breed in streams, whereas the others breed in ponds. The genus is considered to be part of the Middle American Faunal Element; the species are thought to have differentiated in response to ecological diversity and historical opportunities provided by Cenozoic changes in physiography and climate. LITERATURE CITED BAIRD, S. F. 1854. Descriptions of new genera and species of North American frogs. Proc. Acad. Nat. Sci. Philadelphia, 7:59-62. April 27. 1859. Reptiles of the boundary. United States and Mexican boundary survey. Washington, D. C., p. 35, pl. 41. BALDAUF, R. J. 1959. Morphological criteria and their use in showing bufonid phylogeny. Jour. Morph., 104:527-560. May. BARBOUR, T. 1923. Notes on reptiles and amphibians from Panama. Occas. Papers Mus. Zool. Univ. Michigan, 129:1-16. January 25. BLAIR, W. F. 1959. Call structure and species groups in U. S. treefrogs (_Hyla_). Southwest. Nat., 3:77-89. June 1, 1959. 1962. Non-morphological data in anuran classification. Syst. Zool., 11:72-84. June. 1963. Evolutionary relationships of North American toads of the genus Bufo: A progress report. Evolution, 17:1-16. March. BOGERT, C. M. 1960. The influence of sound on the behavior of amphibians and reptiles. _in_ Lanyon, W. E. and Tavolga, W. N. (Eds.) Animal sounds and communication, pp. 137-320. BRATTSTROM, B. H. 1957. The phylogeny of the Salientia based on skeletal morphology. Syst. Zool., 6:70-74. June. BREDER, C. M., Jr.