d
_Tomodactylus_.

At least nine leptodactylid genera are either known or thought to be
terrestrial breeders lacking a free-living tadpole stage
(_Eleutherodactylus_, _Euparkerella_, _Hylactophryne_, _Niceforonia_,
_Noblella_, _Sminthillus_, _Syrrhophus_, _Tomodactylus_ and
_Trachyphrynus_). _Niceforonia_ and _Trachyphrynus_, and probably
_Hylactophryne_, are not closely related to the other genera. Direct
development probably is an adaptation to adverse environmental
conditions since many of the species occur in semi-arid or cold (Andean
paramos) areas. _Eleutherodactylus_ is generally thought to be the
stock from which _Euparkerella_, _Noblella_, and _Sminthillus_ evolved
(Griffiths, 1959) and from which _Syrrhophus_ and _Tomodactylus_ are
derived (Firschein, 1954).

The present distribution of _Hylactophryne_ (isolated on the Mexican
Plateau) and its digital form (like that of Papuan and many primitive
South American leptodactylids) suggest that the genus was isolated in
Mexico throughout the Tertiary, whereas the other Central American
genera are either post-Pliocene derivatives of _Eleutherodactylus_ or
invaders of Central America from South America since the mid-Pliocene
land bridge was formed (Lloyd, 1963).

Piatt (1934) presented arguments against assigning _Eleutherodactylus
latrans_ to the genus _Lithodytes_ and concluded that it was a "true"
_Eleutherodactylus_. Contrary to his arguments, _latrans_ (= _augusti_
of Zweifel) and _E. tarahumarensis_ Taylor differ from all other
_Eleutherodactylus_ (and _Syrrhophus_ and _Tomodactylus_) in the nature
of the tips of the digits (external and skeletal). The digits of
_Hylactophryne_ are like those of _Eupsophus_. My study of nearly all
genera of leptodactylids indicates that Noble (1925) was correct in
suggesting that _Borborocoetes_ (= _Eupsophus_) is a close relative of
_Eleutherodactylus latrans_, although Noble's arguments were based in
part upon false evidence concerning the breeding habits of _E.
latrans_, then thought to have a free-living tadpole.

Kellogg (1932) and Piatt (1934) argued that the terminal phalanges of
_E. latrans_ were typically eleutherodactyline. The variation of this
character in _Eupsophus_ (see Fig. 4) ranges from knobbed to bifurcate
or Y-shaped (T-shaped in _Eleutherodactylus_, _Syrrhophus_ and
_Tomodactylus_) and encompasses the nature of the character represented
in _Hylactophryne_. _Eupsophus_ differs from _Hylactophryne_ in
po