SYSTEMATIC ACCOUNTS 314 _Ptychohyla_ Taylor, 1944 314 Key to Adults 315 Key to Tadpoles 315 _Ptychohyla euthysanota_ Group 315 _Ptychohyla euthysanota_ 315 _Ptychohyla euthysanota euthysanota_ (Kellogg) 315 _Ptychohyla euthysanota macrotympanum_ (Tanner) 320 _Ptychohyla leonhardschultzei_ (Ahl) 323 _Ptychohyla spinipollex_ (Schmidt) 327 _Ptychohyla schmidtorum_ Group 331 _Ptychohyla schmidtorum_ 331 _Ptychohyla schmidtorum schmidtorum_ Stuart 331 _Ptychohyla schmidtorum chamulae_ Duellman 334 _Ptychohyla ignicolor_ Duellman 337 DISTRIBUTION AND ECOLOGY 340 Geographic Distribution of the Species 340 Habitat Preference 342 Interspecific Competition 343 Reproduction and Development 344 PHYLOGENY OF PTYCHOHYLA 345 _Ptychohyla_ as a Natural Assemblage 345 Generic Relationships 346 Interspecific Relationships 347 LITERATURE CITED 349 INTRODUCTION Probably no ecological group of hylid frogs (some _Hyla_ plus _Plectrohyla_ and _Ptychohyla_) in Middle America is so poorly known as those species that live in the cloud forests on steep mountain slopes and breed in cascading mountain streams. During the last half of the nineteenth century most of the species of hylids living in the lowlands of southern Mexico and northern Central America were named and described. Despite the extensive collecting by Salvin and Godman, Nelson and Goldman, and the various expeditions of the _Mission Scientifique_, no members of the genus _Ptychohyla_ were obtained until 1927, when in the mountains of El Salvador Ruben A. Stirton found a small tree frog that subsequently was described and named _Hyla euthysanota_ by Kellogg (1928). Until recently frogs of this genus were known from few specimens and in the literature by nearly as many names.