Taylor (1952) synonymized _Engystomops_ with _Eupemphix_ which, although related, should be regarded as generically distinct (Gallardo, 1965). Perhaps the most conservative classification is that of Myers (1962) who, without published evidence, combined _Eleutherodactylus_, _Syrrhophus_, and the South American _Lithodytes_ in a single genus. The major problem for students working with the Mexican leptodactylids has not been the separation of _Engystomops_ or _Leptodactylus_ from other genera but the separation and definition of the eleutherodactyline frogs currently placed in three genera, _Eleutherodactylus_, _Syrrhophus_, and _Tomodactylus_. As will be shown in this paper, these are more conveniently placed in four genera. Once a fourth genus is recognized, certain phylogenetic problems disappear and a reasonable zoogeographic interpretation is possible for Middle American leptodactylid distribution. ANALYSIS OF CHARACTERS In Mexico and northern Central America approximately 55 species of eleutherodactyline frogs (_Eleutherodactylus_, _Syrrhophus_, and _Tomodactylus_) are known. Four genera can be recognized on the basis of the nature of inguinal glands, morphology of the hands and feet, and certain osteological features. [Illustration: FIG. 1. _Tomodactylus angustidigitorum_ (UMMZ 114305, x 4.5) illustrating the lumbo-inguinal gland typical of members of the genus. From a kodachrome by Wm. E. Duellman.] Glands Leptodactylids have a variety of glands that have been used as generic characters. Smith and Taylor (1948) regarded the so-called inguinal gland as a generic character in Mexican eleutherodaycty-lines. Lynch (1965) showed that _Eleutherodactylus_ and _Microbatrachylus_ cannot be separated by the nature of the gland or the condition of the prevomers (dentate or not). _Syrrhophus_ and _Tomodactylus_, as defined by Smith and Taylor (1948), are not generically distinct because of overlap in the condition of the prevomers and in the development of the gland. Firschein (1954) stated that _Syrrhophus_ differed from _Tomodactylus_ by having an axillary gland, but it is now known that one species of _Syrrhophus_ lacks the gland. The inguinal glands of _Eleutherodactylus_ and _Syrrhophus_, if present, are diffuse, irregular in outline, and generally not prominent; in _Tomodactylus_ the gland is higher on the body (a lumbo-inguinal gland), compact, oval in outline, and prominent (Fig. 1). Axillary glands occur in most _Syrrhophus_ but are not known in _Tomodactylus_ or _Eleutherodactylus_. Hands and feet The tips of the digits are laterally expanded in most _Eleutherodactylus_, _Syrrhophus_, and _Tomodactylus_. Two species of _Eleutherodactylus_ (_augusti_ and _tarahumarensis_) and two _Tomodactylus_ (_angustidigitorum_ and _grandis_) lack any expansion of the digital tips. All but two of the species of eleutherodactyline frogs (_E. augusti_ and _E. tarahumarensis_) have a transverse groove across the tips of the digits (Fig. 2).