All individuals were found in trees and bushes near streams in cloud forest at night in February. The type locality is the same as that of _Hyla pentheter_ and _Hyla thorectes_, discovered by Kraig Adler in June, 1964. Our field work there in February, 1966, resulted in finding _Hyla altipotens_, _H. pellita_, and _Ptychohyla leonhardschultzei_, but no individuals of the species found by Adler. A visit to the same locality in August, 1966, revealed no individuals of either _H. altipotens_ or _pellita_; instead _pentheter_ and _thorectes_ were found along the stream. Duellman (1965:166) listed a specimen (TCWC 16184) of _Hyla chaneque_ from Los Fustes, 3 kilometers east of San Sebastian, Oaxaca. Reexamination of this specimen reveals that it is _Hyla altipotens_. The frog was obtained by Dilford Carter on April 29, 1960; it was under a rock at the edge of a stream in an oak-pine-cypress association at an elevation of 1800 meters. The specific name _altipotens_ is Latin, meaning mighty, here used in allusion to the supposed potentiality of fertilization by the production of vast quantities of sperm in the large testes. Plectrohyla hartwegi new species Plate 19 _Holotype._--Adult male, UMMZ 94428, from Barrejonel (19 kilometers west of Chicomuselo), Chiapas, Mexico, elevation 1000 meters, obtained on June 12, 1941, by Eizi Matuda. _Paratypes._--Two subadult males, KU 58873 from Paraje El Triunfo, north of Mapastepec, Chiapas, Mexico, elevation 2050 meters, obtained on May 12, 1960, by Miguel Alvarez del Toro, and UIMNH 40837 from Cerro Azul Oaxaca, Mexico, obtained on March 7, 1956, by Thomas MacDougall. _Diagnosis._--A _Plectrohyla_ having a bifid prepollex, bold mottling on flanks and ventral surfaces of shanks, and vertical dark bars on anterior and posterior surfaces of thighs, and lacking vocal slits and outer tarsal fold.