_Osteocephalus leprieurii_ differs from all other members of the genus by having transverse dark bars on the back. Two other hylids (_Hyla lanciformis_ and _multifasciata_) in the Amazon Basin have transverse dark marks on the dorsum. Both of these differ from _leprieurii_ by having pointed snouts, much longer hind limbs, and smooth skin dorsally. _Distribution._--The periphery of the Amazon Basin, in the Guianas and the upper part of the basin in southern Colombia, Ecuador, Peru, and extreme western Brasil (Fig. 9). Most localities are at elevations of less than 500 m, but the species ascends the lower Andean slopes to elevations of 1100 m. 265 specimens from 31 localities. [Illustration: FIG. 9. Distribution of _Osteocephalus leprieurii_ (circles) and _O. verrucigerus_ (triangles).] _Remarks._--Most adults of _leprieurii_ have distinct transverse markings on the back; these are variable in width, extent, and arrangement. In some specimens, such as USNM 166557, some of the transverse bars are fragmented into spots; in a few specimens the dorsal pattern consists solely of small dark spots arranged in transverse rows. Such specimens have a dorsal pattern resembling that of some _taurinus_. The transverse nature of the dorsal markings is further modified in some specimens, such as USNM 166555, in which the dark bars are fragmented and oblique. Extreme ontogenetic change in color pattern is exhibited by this species (Fig. 10). Juveniles having snout-vent lengths of less than 28 mm have an olive-brown dorsum with a pale cream stripe across the head and broad, cream, dorsolateral stripes; transverse dark bars are absent on the body and limbs. Individuals having snout-vent lengths of 30-35 mm have dark brown transverse bars on the back and limbs but still retain the light dorsolateral stripes, whereas the stripes are lost in larger individuals. [Illustration: FIG. 10. Ontogenetic change in color pattern in _Osteocephalus leprieurii_: a. KU 126644; b. KU 126640; c. KU 126625. x2.] Coloration in life of specimens from Lago Agrio, Ecuador: "In males the dorsal ground color varies from dark brown to ochre-tan; dorsal markings uniformly dark brown. Most specimens have dark brown and cream anal stripes; labial area cream-colored. Flanks vary from tan to white. Ventral coloration varies from salmon to tan to white. The iris is bronze with a greenish cast and black reticulations. In females the dorsal coloration is the same as in males, except that dark marks tend to be outlined with cream; venter tannish salmon." (W. E. Duellman, field notes, 12 May 1969). =Osteocephalus pearsoni= (Gaige) _Hyla pearsoni_ Gaige, 1929:3 [Holotype.--UMMZ 57548 from the upper Rio Beni, below mouth of Rio Mapiri, Departamento El Beni, Bolivia; N. E. Pearson collector]. _Osteocephalus pearsoni_--Goin, 1961:13.