Measurements were taken in the manner described by Duellman (1956). Osteological data were obtained from specimens that were cleared in potassium hydroxide, stained with alizarin red, and stored in glycerine. Recordings were made by means of Magnemite portable tape recorders (Amplifier Corp. America). The calls recorded by Fouquette were analyzed on a Sonagraph (Kay Electric Co.) at the University of Texas; those recorded by Duellman were analyzed mainly on a Vibralyzer (Kay Electric Co.) at the University of Kansas and in part on a Sonagraph at the University of Southwestern Louisiana. Sample calls were analyzed on all three instruments; the slight differences in results were found to be less than the error in measurement, so the data from all sources were combined without correction. The techniques and terminology of the calls are those defined by Fouquette (1960a, 1960b). In the accounts of the species we have attempted to give a complete synonymy. At the end of each species account the localities from which specimens were examined are listed alphabetically within each state, province, or department, which in turn are listed alphabetically within each country. The countries are arranged from north to south. Localities preceded by an asterisk (*) are not plotted on the accompanying maps due to the crowding of symbols that would have resulted. Abbreviations for museum specimens are listed below: AMNH --American Museum of Natural History ANSP --Academy of Natural Sciences of Philadelphia BMNH --British Museum (Natural History) BYU --Brigham Young University CAS --California Academy of Sciences FMNH --Field Museum of Natural History KU --University of Kansas Museum of Natural History MCZ --Museum of Comparative Zoology MVZ --Museum of Vertebrate Zoology SU --Stanford University UIMNH--University of Illinois Museum of Natural History UMMZ --University of Michigan Museum of Zoology USC --University of Southern California USNM --United States National Museum UU --University of Utah TCWC --Texas Cooperative Wildlife Collection TNHM --Texas Natural History Museum HYLA MICROCEPHALA GROUP