In the mountainous regions of Middle America there are several groups
of hylid frogs that inhabit mountain streams. Some of these groups,
such as _Plectrohyla_ and _Ptychohyla_, have been elevated to generic
rank, whereas others are retained in the large and complex genus
_Hyla_. In the mountains of Mexico five species of hylids that seem to
compose a phyletic unit are herein referred to as the _Hyla bistincta_
group. Since 1955 I have been accumulating specimens of, and data on,
this group with the result that all specimens known to me, including
the types of all named taxa, have been studied. Detailed observations
have been made on the ecology and life histories of three of the
species; the other two species are known to me only from preserved
specimens.