When we initiated a study of the herpetofauna at Santa Cecilia in Amazonian Ecuador in 1966, we were immediately confronted with many kinds of animals that we could not identify with the existing literature. Comparisons of our specimens with those preserved in other museums resolved some of the problems, but many identifications could be made only after study of type specimens; even then some determinations remained questionable. We now find that in order to prepare a meaningful account of the herpetofauna of Santa Cecilia, we must complete several taxonomic studies, the limits of which extend far beyond eastern Ecuador. Because of our interests in hylids we have begun our studies on these frogs.
One of us (Trueb, 1970a) studied the cranial osteology of casque-headed hylid frogs and redefined the genus Osteocephalus but did not determine the number of species in the genus. Our work in Amazonian Ecuador resulted in the discovery of the sympatric occurrence of three species at each of two localities; one of these species was found with a fourth species at another locality. Study of museum specimens confirmed the recognition of these four species in the Amazon Basin and lower Amazonian slopes of the Andes. A fifth species from Bolivia and Perú also is included in the genus. Examination of museum specimens has provided data on the geographic variation in, and distribution of, the five species. However, our conclusions pertaining to some populations need substantiation, because we have been hampered by inadequate material from areas beyond Ecuador. More than half of the 905 specimens of Osteocephalus are from Ecuador, a relatively small part of the total range of the genus.
In this paper we are presenting a taxonomic review of the genus Osteocephalus; of necessity our study has been at the alpha level. We have utilized all of the usual external characters, as well as osteological features in our definitions of the species. Tadpoles and mating calls are available for only one species, O. verrucigerus (Trueb and Duellman, 1970); these and other important systematic characters, such as karyotypes, are not available for the group at this time. Our tendency has been to take a conservative view of species; thus it is doubtful that any subsequent worker will recognize fewer species in the genus. Our observations on these frogs in Amazonian Ecuador are presented in a final section of this paper.
ACKNOWLEDGMENTS
For the loan of specimens or for the provision of working space in their respective institutions, we are indebted to James E. Böhlke, Werner C. A. Bokermann, F. W. Braestrup, Nelly Carrillo de Espinoza, Osvaldo R. da Cunha, Josef Eiselt, M. J. Fouquette, Jr., Alice G. C. Grandison, Jean Guibé, Birgitta Hansson, Walter Hellmich, M. J. Hoogmoed, Robert F. Inger, Konrad Klemmer, Jean Lescure, Alan E. Leviton, Clarence J. McCoy, Robert H. Mount, Charles W. Myers, Umberto Parenti, Günther Peters, James A. Peters, William F. Pyburn, Juan A. Rivero, Dorothy M. Smith, Paulo E. Vanzolini, Greta Vestergren, David B. Wake, Charles F. Walker, Ernest E. Williams, and Richard G. Zweifel.
Study of specimens in European museums was made possible by a grant (No. 5063) from the Penrose Fund of the American Philosophical Society. Field work in Ecuador was partially supported by grants from the Watkins Fund of the Museum of Natural History, University of Kansas. At our base camp at Santa Cecilia, Ecuador, we enjoyed the hospitality of Ing. Ildefonso Muñoz B. Transportation in Ecuador was generously provided by the Texaco Petroleum Company. During the course of our field work Stephen R. Edwards and Thomas H. Fritts contributed directly to our study of Osteocephalus. Michael J. Tyler of the South Australian Museum provided information on the vocal sac structure. We extend our sincere thanks to all of these persons for their contributions to our endeavors.
MATERIALS AND METHODS
We have examined 893 preserved frogs, including the type specimens of all included nominal taxa, 8 skeletons, 1 lot of eggs, and 3 lots of tadpoles that we refer to the genus Osteocephalus; in addition skulls were removed from five preserved specimens, and radiographs were made of 12 other preserved specimens. We have been fortunate in seeing living individuals of all species, except O. pearsoni, but we have colored photographs of a living specimen of that species. Figures [1] and [2] were drawn from projected colored transparencies of living frogs. Terminology follows that of Duellman (1970b). On the distribution maps solid symbols indicate localities from which we have examined specimens; open symbols represent additional locality records based on the literature. Throughout the text specimens are listed by their catalogue numbers preceded by the appropriate museum abbreviation, as follows:
| AMNH | American Museum of Natural History |
| ANSP | Academy of Natural Sciences of Philadelphia |
| ASU | Arizona State University |
| AUM | Auburn University Museum |
| BMNH | British Museum (Natural History) |
| CAS | California Academy of Sciences |
| CAS-SU | Stanford University Collection (In California Academy of Sciences) |
| CM | Carnegie Museum |
| FMNH | Field Museum of Natural History |
| KU | University of Kansas Museum of Natural History |
| MCZ | Museum of Comparative Zoology, Harvard University |
| MIZS | Museo ed Istituto di Zoologi Sistematico, Università di Torino |
| MJP | Museo Javier Prado, Lima |
| MNHN | Muséum National d'Histoire Naturelle, Paris |
| MPEG | Museu Paraense Emiliano Goeldi, Belém |
| MVZ | Museum of Vertebrate Zoology, University of California, Berkeley |
| MZUSP | Museu de Zoología, Universidade da São Paulo |
| NHMG | Naturhistoriska Museet Göteborg |
| NHMW | Naturhistorisches Museum, Wien |
| NHRM | Naturhistoriska Riksmuseet, Stockholm |
| RMNH | Rijksmuseum van Natuurlijke Histoire, Leiden |
| SMF | Senckenbergische Museum, Frankfurt |
| UIMNH | University of Illinois, Museum of Natural History |
| UMMZ | University of Michigan Museum of Zoology |
| UP | Université de Paris |
| UPR-M | University of Puerto Rico, Mayagüez |
| UTA | University of Texas, Arlington |
| USNM | United States National Museum |
| UZM | Universitets Zoologiske Museum, Copenhagen |
| WCAB | Werner C. A. Bokermann, São Paulo, Brasil |
| ZMB | Zoologisches Museum Berlin |
| ZSM | Zoologisches Sammlung München |