atis_, and _vaillanti_). Adequate material is not
available for detailed study of all South American species;
consequently, a firm classification cannot be established at this time.
Nevertheless, it is obvious that Lutz's arrangement is unnatural. If
subsequent investigations show, as seems likely, that the small
specialized phyllomedusines are a natural phyletic unit, the generic
name _Pithecopus_ is available. However, species such as _boliviana_,
_burmeisteri_, _nicefori_, and _trinitatis_ do not belong in
_Pithecopus_. As noted by Funkhouser (1962), the small, relatively
unspecialized species (_lemur_, _loris_, and _medinae_) form a natural
group; possibly this group should be accorded generic recognition. Until
more evidence on the interspecific relationships is acquired, the
maintenance of the current classification is desirable.

DISCUSSION

Noble (1931) considered the species of _Phyllomedusa_ having opposable
digits, reduced terminal discs, and no webbing to be advanced and such
species as _Agalychnis moreleti_, _calcarifer_, and _spurrelli_ to be
primitive. Funkhouser (1957) followed Noble's suggestion and attempted
to explain the evolution of the species of _Phyllomedusa_ (_sensu lato_)
by assuming that they evolved from an advanced _Hyla_-like ancestor.
Therefore, she placed those species having large, fully webbed hands and
feet near the base of her phylogenetic scheme and hypothesized that
evolutionary sequences involved stages of reduction and eventual loss of
webbing, followed by the development of grasping toes. Such an
evolutionary history is highly unlikely. The _Agalychnis_ phyletic line
has one kind of specialization for an arboreal existence. It is contrary
to evolutionary theory that a specialized group would evolve into a
generalized form and then evolve new kinds of specializations to meet
the needs imposed by the same environmental conditions affecting the
earlier specialized group. A more reasonable hypothesis is that the
evolution of opposable digits took place in a phyletic line that had as
its ancestral stock a frog with generalized hands and feet. If this
assumption is correct, _Phyllomedusa_ and _Agalychnis_ represent
different phyletic lines; each exhibits divergent modes of adaptation
for arboreal habits, whereas _Pachymedusa_ probably remains relatively
little changed from the basic phyllomedusine stock.

On the basis of modern distribution and areas of diversification alone
(no f