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 possessing a frontoparietal fontanelle, in generally having a maxillary-quadratojugal gap, and in having a free swimming tadpole stage. [Illustration: FIG. 5. Outline drawings of _Leptodactylus melanonotus_ (left, KU 65704, x 2) and _Eleutherodactylus alfredi_ (right, KU 93994, x 2).] KEY TO MEXICAN LEPTODACTYLID GENERA 1. Small (20-40 mm.), pustular, toadlike frogs; maxillary and premaxillary bones not bearing teeth _Engystomops_