According to the most recent review of the Mexican amphibian fauna (Smith and Taylor, 1948), six genera of leptodactylid frogs occur in México. One other genus, _Pleurodema_, occurs in Lower Central America. Smith and Taylor recognized one species of _Engystomops_, 28 of _Eleutherodactylus_, three of _Leptodactylus_, eight of _Microbatrachylus_, 12 of _Syrrhophus_, and five of _Tomodactylus_. Subsequent to the publication of their checklist of the Mexican amphibia (1948), numerous taxonomic changes have been proposed. Many species of _Eleutherodactylus_ have been added to the fauna, either through the extension of their recorded ranges into México from Guatemala or by the recognition of species unknown in 1948, whereas some nominal species have been synonymized. _Microbatrachylus_ has been regarded as synonymous with _Eleutherodactylus_ (Lynch, 1965); four species of _Microbatrachylus_ currently are regarded as valid (Duellman, 1961, Lynch, 1965). _Syrrhophus_ was revised in part by Duellman (1958) and Firschein (1954), and a species of _Tomodactylus_ transferred to _Syrrhophus_ by Dixon (1957), who redefined _Tomodactylus_ and added more species to the genus.

Since beginning my studies of the Mexican leptodactylids in 1962, I have become acutely aware of difficulties involved in defining the genera. A revision of _Eleutherodactylus_ and a review of _Syrrhophus_ are nearing completion, but prior to their publication it is desirable to redefine the genera of the Mexican leptodactylids, and in so doing recognize an heretofore unnamed genus. The definitions of _Eleutherodactylus_ and _Leptodactylus_ may need to be altered in the future, since both are widespread in South America and occur in the West Indies. Their definitions as given here are as precise as present knowledge permits. _Syrrhophus_ and _Tomodactylus_ are small assemblages that occur only in southwestern United States, México, and Guatemala.