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INTRODUCTION

The tree frogs of the _Hyla rubra_ group are abundant and form a
conspicuous element of the Neotropical frog fauna. Representatives of
the group occur from lowland Mexico to Argentina; the greatest
diversity is reached in the lowlands of southeastern Brazil (Cochran,
1955). The group apparently originated in South America; the endemic
Central American species evolved from stocks that invaded Middle
America after the closure of the Colombian Portal in the late Pliocene.

Dunn (1933) partially defined the _rubra_ group as it occurs in Central
America. Cope (1865, 1876, 1887), Brocchi (1881), Boulenger (1882),
Guenther (1901), Noble (1918), Kellogg (1932), Dunn and Emlen (1932),
Stuart (1935), and Gaige (1936) dealt with the Middle American species
now considered to make up the _rubra_ group. More recently, Taylor
(1952, 1958), Fouquette (1958), Starrett (1960), and Duellman (1960,
1963, 1966a) studied aspects of the taxonomy and biology of the species
of this group. The five species of the _rubra_ group in Central America
have received ten different names. One species, _Hyla staufferi_, has
received five names (two subspecies are recognized herein). _Hyla
boulengeri_ was named in the genus _Scytopis_, but the type species of
_Scytopis_ is a member of the genus _Phrynohyas_ Fitzinger, 1843
(Duellman, 1956.)

Little has been published concerning the ecology, life history,
osteology, and mating calls of the Middle American species of this
group. The purpose of the present report is to describe the species
occurring in Middle America and to comment on their distributions,
ecology, cranial osteology, and mating calls, and in so doing provide
evidence for the evolutionary history of the species inhabiting Middle
America.

Acknowledgments

For permission to examine specimens in their care, I am grateful to
Drs. Richard G. Zweifel, American Museum of Natural History (AMNH);
Robert F. Inger, Field Museum of Natural History (FMNH); Ernest E.
Williams, Museum of Comparative Zoology (MCZ); Hobart M. Smith,
University of Illinois Museum of Natural History (UIMNH); Charles F.
Walker, University of Michigan Museum of Zoology (UMMZ); Jay M. Savage,
University of Southern California (USC); James A. Peters, United States
National Museum (USNM); Richard J. Baldauf, Texas Cooperative Wildlife
Collection (TCWC); and W. Frank Blair, Texas Natural History Collection
(TNHC). KU refers