All Mexican eleutherodactyline frogs have quadratojugal-maxillary articulations, completely roofed skulls in adults, median contact of the nasals, separated occipital condyles, and large prevomers. The premaxillae of all species are visible when the skulls are viewed from directly above. The pterygoid lacks a medioventral flange and does not meet the palatine. In no species is the anterior arm of the squamosal in contact with the maxillary. Of the numerous species examined (30 _Eleutherodactylus_, four _Syrrhophus_, and four _Tomodactylus_), the species in the _Eleutherodactylus augusti_ group are unique in having a sphenethmoid with a blunt anterior edge. Pectoral Girdle All species have large cartilaginous plates in the pectoral girdles; none possesses a bony style. No divergent modifications of the clavicle and coracoid bones are known in the family. GENERIC ACCOUNTS Genus ~Eleutherodactylus~ Dumeril and Bibron, 1841 _Type-species._--_Hylodes martinicensis_ Tschudi, 1838 _Diagnosis and definition._--Small to large frogs (12 to 110 mm. snout-vent length) having slightly to widely expanded digital pads, each pad bearing a terminal transverse groove; lumbo-inguinal, inguinal, and axillary glands absent, or if present, diffuse, irregular in outline, not compact; plantar supernumerary tubercles absent, or if present, six or fewer, restricted to distal area of plantar surface, and not extending between metatarsal tubercles; tarsus bearing inner or outer tubercles or folds or not; toes free to one-half webbed; terminal phalanges T-shaped; sternum cartilaginous, lacking bony style; sphenethmoid not truncate anteriorly; nasals in contact medially; maxillary and quadratojugal in contact; anterior arm of squamosal not in contact with maxillary; dermal cranial elements not involved in integumentary-cranial co-ossification; prevomers large, dentigerous processes present or not, dentate or not; maxillary and premaxillary bones dentate; occipital condyles separated; development direct. _Composition._--About 420 names have been applied to frogs of this genus; many of these names are synonyms, and many other species remain undescribed and unnamed. Perhaps the genus contains 350 species. Thirty-one species occur in Mexico and northern Central America. _Distribution._--From Tamaulipas and Sinaloa, Mexico, exclusive of the Mexican Plateau, to at least Peru and southernmost Brazil and throughout the West Indies. Introduced into Florida. _Etymology._--Greek (_eleuthero_ + _dactylus_) meaning free-toed. Genus ~Engystomops~ Jimenez de la Espada, 1872 _Type species._--_Engystomops petersi_ Jimenez de la Espada, 1872