Among the amphibians sent to the Museum National d'Histoire Naturelle in Paris by a Monsieur Leprieur in French Guiana was a single female specimen of a moderately large hylid having a well-ossified skull and smooth dorsal skin. This specimen escaped from the covetous eyes of Johann Tschudi, who prematurely named several species on the basis of specimens in Paris, and survived without an epithet until Dumeril and Bibron (1841) proposed for it the name _Hyla leprieurii_. The description of the species is fairly detailed, but the specimen was not illustrated. This is the earliest trivial name now associated with _Osteocephalus_. Fitzinger (1843) in his generic synopsis of amphibians and reptiles proposed the generic name _Osteocephalus_ but did not associate a specific name with the genus. Consequently, _Osteocephalus_ Fitzinger, 1843, is a _nomen nudum_. Franz Steindachner followed Leopoldo Fitzinger at the Naturhistorisches Museum in Vienna, where he had access to Fitzinger's notes and, of course, the important collections housed in that museum. Steindachner (1862) named two species of _Osteocephalus_ on the basis of Brasilian specimens collected by Johann Natterer. Both species were named in the same publication; _O. taurinus_ appeared on page 77, and _O. favolineatus_, on p. 80. This is the earliest association of the generic name _Osteocephalus_ with a specific name and a description, both of which satisfy the Code of Zoological Nomenclature for generic availability. Therefore, Steindachner is the authority for the generic name _Osteocephalus_, which has _O. taurinus_ as the type species by original designation. It is not possible to determine whether or not Steindachner's usage of _Osteocephalus_ was the same as that intended by Fitzinger 19 years earlier. Steindachner (1862) gave reasonably good descriptions of his two new species and provided excellent illustrations of the two specimens, both large females. Apparently impressed by the similarities between _Trachycephalus nigromaculatus_ Tschudi, 1838, and _Osteocephalus taurinus_, Steindachner (1867) used the combination _Trachycephalus (Osteocephalus) taurinus_. This ambiguous usage for the 1860's precludes our determining if Steindachner was in effect synonymizing _Osteocephalus_ with _Trachycephalus_ or whether he was placing _Osteocephalus_ in a subgeneric status. Steindachner (1867) did not mention _O. flavolineatus_; perhaps by that time he had concluded that _flavolineatus_ was only a color morph of _taurinus_. Cope (1867) placed _Hyla leprieurii_ in the genus _Hypsiboas_ Wagler, 1830. Cope (1874) named _Osteocephalus planiceps_ from Nauta, Peru. The single specimen was among the collections made by the Orton Expedition to the upper Amazon Basin and was deposited in the Academy of Natural Sciences in Philadelphia.