The definition of genera in the family Hylidae is difficult owing to the vast array of species, most of which are poorly known as regards their osteology, colors in life, and modes of life history. The genera Diaglena, Triprion, Tetraprion, Osteocephalus, Trachycephalus, Aparasphenodon, Corythomantis, Hemiphractus, Pternohyla, and Anotheca have been recognized as distinct from one another and from the genus Hyla on the basis of various modifications of dermal bones of the cranium. Phyllomedusa is recognized on the basis of a vertical pupil and opposable thumb; Plectrohyla is characterized by the presence of a bony prepollex and the absence of a quadratojugal. Gastrotheca is distinguished from other hylids by the presence of a pouch in the back of females. A pair of lateral vocal sacs behind the angles of the jaws and the well-developed dermal glands were used by Duellman (1956) to distinguish Phrynohyas from Hyla. He (1963a) cited the ventrolateral glands in breeding males as diagnostic of Ptychohyla. Some species groups within the vaguely defined genus Hyla have equally distinctive characters. The Hyla septentrionalis group is characterized by a casque-head, not much different from that in the genus Osteocephalus (Trueb, MS). Males in the Hyla maxima group have a protruding bony prepollex like that characteristically found in Plectrohyla.
Ontogenetic development, osteology, breeding call, behavior, and ecology are important in the recognition of species. By utilizing the combination of many morphological and biological factors, the genus Smilisca can be defined reasonably well as a natural, phyletic assemblage of species. Because the wealth of data pertaining to the morphology and biology of Smilisca is lacking for most other tree frogs in Middle America it is not possible at present to compare Smilisca with related groups in more than a general way.
Smilisca is an excellent example of an Autochthonous Middle American genus. As defined by Stuart (1950) the Autochthonous Middle American fauna originated from "hanging relicts" left in Central America by the ancestral fauna that moved into South America and differentiated there at a time when South America was isolated from North and Middle America. The genus Smilisca, as we define it, consists of six species, all of which occur in Central America. One species ranges northward to southern Texas, and one extends southward on the Pacific lowlands of South America to Ecuador. We consider the genus Smilisca to be composed of rather generalized hylids. Consequently, an understanding of the systematics and zoogeography of the genus can be expected to be of aid in studying more specialized members of the family.
Examination of many of the specimens used in our study was possible only because of the cooperation of the curators of many systematic collections. For lending specimens or providing working space in their respective institutions we are grateful to Doris M. Cochran, Alice G. C. Grandison, Jean Guibe, Robert F. Inger, Günther Peters, Gerald Raun, William J. Riemer, Jay M. Savage, Hobart M. Smith, Wilmer W. Tanner, Charles F. Walker, Ernest E. Williams, and Richard G. Zweifel.
We are indebted to Charles J. Cole and Charles W. Myers for able assistance in the field. The cooperation of Martin H. Moynihan at Barro Colorado Island, Charles M. Keenan of Corozal, Canal Zone, and Robert Hunter of San José, Costa Rica, is gratefully acknowledged. Jay M. Savage turned over to us many Costa Rican specimens and aided greatly in our work in Costa Rica. James A. Peters helped us locate sites of collections in Ecuador and Coleman J. Goin provided a list of localities for the genus in Colombia.
We especially thank Charles J. Cole for contributing the information on the chromosomes, and Robert R. Patterson for preparing osteological specimens. We thank M. J. Fouquette, Jr., who read the section on breeding calls and offered constructive criticism.
Permits for collecting were generously provided by Ing. Rodolfo Hernandez Corzo in México, Sr. Jorge A. Ibarra in Guatemala, and Ing. Milton Lopez in Costa Rica. This report was made possible by support from the National Science Foundation (Grants G-9827 and GB-1441) and the cooperation of the Museum of Natural History at the University of Kansas. Some of the field studies were carried out in Panamá under the auspices of a grant from the National Institutes of Health (NIH GM-12020) in cooperation with the Gorgas Memorial Laboratory in Panamá.