Probably no ecological group of hylid frogs (some _Hyla_ plus
_Plectrohyla_ and _Ptychohyla_) in Middle America is so poorly known
as those species that live in the cloud forests on steep mountain
slopes and breed in cascading mountain streams. During the last half
of the nineteenth century most of the species of hylids living in the
lowlands of southern Mexico and northern Central America were named
and described. Despite the extensive collecting by Salvin and Godman,
Nelson and Goldman, and the various expeditions of the _Mission
Scientifique_, no members of the genus _Ptychohyla_ were obtained
until 1927, when in the mountains of El Salvador Ruben A. Stirton
found a small tree frog that subsequently was described and named
_Hyla euthysanota_ by Kellogg (1928). Until recently frogs of this
genus were known from few specimens and in the literature by nearly as
many names.
Although I first collected _Ptychohyla_ in 1956, it was not until 1960
that special efforts were made to obtain specimens of this genus. The
summer of 1960 was spent in southern Mexico and Guatemala, where every
accessible stream in the cloud forests was searched for tree frogs,
especially _Ptychohyla_ and _Plectrohyla_. Similar, but less
extensive, investigations were carried out in 1961 and 1962. The
result of this field work is a rather large collection of _Ptychohyla_
representing all of the known species, plus tape recordings of the
breeding calls and tadpoles of all of the species.
Previously, I have discussed the nomenclature of one of the species
(Duellman, 1960) and have described two new species (Duellman, 1961).
In the latter paper I made reference to a future account (this one)
that would deal with the systematics and biology of the entire genus.
Although I have series of specimens, tadpoles, osteological
preparations, and recordings of breeding calls, thereby having a wide
array of data at my disposal, much still remains to be learned about
these frogs, especially about various aspects of their life histories.
Even the validity of the genus is open to question; this problem is
discussed at length in the section beyond entitled "_Ptychohyla_ as a
Natural Assemblage."