The genus _Syrrhophus_ has been defined (Lynch, 1968) and limited to the group of species occurring in Guatemala, Mexico and the United States. The closest relatives of _Syrrhophus_ are the frogs of the genus _Tomodactylus_ (Dixon, 1957; Firschein, 1954). Lynch (1968) implied there were no osteological bases for the separation of _Eleutherodactylus_, _Syrrhophus_, and _Tomodactylus_. At that time, I believed such to be the case and derived _Syrrhophus_ and _Tomodactylus_ from the _rhodopis_ complex of _Eleutherodactylus_, with which they share terrestrial habits and relatively short limbs. In the _rhodopis_ complex there is a tendency for the loss of the outer palmar tubercle, a not uncommon condition in _Syrrhophus_ and _Tomodactylus_. However, the skulls of _Syrrhophus_ and _Tomodactylus_ show departures from the pattern observed in the Middle American _Eleutherodactylus_, as well as many of those species in western South America. Baldauf and Tanzer (1965) reported that the frontoparietals and prootics were fused in _Syrrhophus marnockii_ and that the prootics and exoccipitals appeared to be one bone (otoccipital). The otoccipital is not uncommon in eleutherodactyline frogs, but the fusion of the frontoparietals with the prootics (regardless of the fusion of the latter with the exoccipital) is uncommon in the family. I have found the frontoparietal-prootic fusion only in _Syrrhophus_ (all species), _Tomodactylus_ (all species), and _Eleutherodactylus_ (West Indies species). None of the Middle American _Eleutherodactylus_ has the two bones fused. Examination of the character is difficult in dried skeletal preparations. Cleared and stained or macerated preparations are satisfactory for checking this character. Thus, in addition to the presence of numerous plantar supernumerary tubercles in the frogs of the genera _Syrrhophus_ and _Tomodactylus_, these two genera can be separated from other Middle American eleutherodactylines by the fusion of the frontoparietals and prootics. This character not only further strengthens the argument that the two genera are closely related but poses a problem of zoogeographic analysis of the distribution of the character, which will be discussed fully elsewhere. Key to the Species of the Frog Genus _Syrrhophus_ 1. Three large, well-developed palmar tubercles 2 Two large palmar tubercles; outer (third) palmar tubercle reduced in size or absent 9 2. Digital pads more than twice (usually three or more) times width of digit 3 Digital pads less than twice width of digit 4 3. Males having vocal slits; dorsum vermiculate; diameter of tympanum in males about one-half diameter of eye _S. dennisi_