The affinities of _Ptychohyla_ apparently are not with any of the other groups that have been generically separated from _Hyla_. Of the daughter genera in Middle America only _Plectrohyla_ has stream-adapted tadpoles, but these large frogs are not closely related to _Ptychohyla_. Stuart (1954:169) suggested that certain montane species of _Hyla_ in lower Central America and _Hyla salvadorensis_ in El Salvador may be related to _Ptychohyla_ or even congeneric. I have had experience with most of these species in the field and believe that Stuart was correct in his suggestion of relationships. The species concerned are four red-eyed stream-breeding _Hyla_ in Costa Rica--_H. alleei_, _H. legleri_, _H. rufioculis_, and _H. uranochroa_, plus _Hyla salvadorensis_ in the mountains of El Salvador. Morphologically all of the species are similar; _Hyla uranochroa_, _H. legleri_, and _H. rufioculis_ have a lateral white stripe that is expanded to form a spot beneath the eye, as in _Ptychohyla schmidtorum_. The tadpoles of _Hyla rufioculis_ and _H. uranochroa_ have large funnel-shaped mouths and long slender tails like those of _Ptychohyla schmidtorum_. Lips of the tadpoles of _H. legleri_ and _H. salvadorensis_ are folded laterally, in this respect resembling those of the _Ptychohyla euthysanota_ group. I do not know the tadpoles and the breeding call of _Hyla alleei_. The breeding calls of _Hyla rufioculis_ and _H. uranochroa_ consist of high melodious notes; the calls of _H. legleri_ and _H. salvadorensis_ consist of series of short notes that have the general characteristics of the call of _Ptychohyla schmidtorum_. Affinities of the genus _Ptychohyla_ seem to me to be with the red-eyed species forming the _Hyla uranochroa_ group in Costa Rica. All of the species in the _Hyla uranochroa_ group have large frontoparietal fontanelles, rather small ethmoids, and small nasals that are not in contact with one another or with the ethmoid. Some species have a complete quadratojugal-maxillary arch; others do not. Assuming that the parental stock that gave rise both to the _Hyla uranochroa_ group and to _Ptychohyla_ was widespread in Central America at a time of cooler, more humid conditions, it is possible that with subsequent warming temperatures and seasonal rainfall in the lowlands the parental stock was restricted to the Costa Rican highlands, where the _Hyla uranochroa_ group developed, and to the Chiapas-Guatemala highlands, where _Ptychohyla_ evolved. Interspecific Relationships