_Content._--As defined here, the genus contains five known species: _O. buckleyi_ (Boulenger), _O. leprieurii_ (Duméril and Bibron), _O. pearsoni_ (Gaige), _O. taurinus_ Steindachner, and _O. verrucigerus_ (Werner).
_Distribution._--The Guianas and Amazon Basin; also in the upper Orinoco and Magdalena drainages. Most localities are at elevations below 500 m, but the genus ascends the Amazonian slopes of the Andes to elevations of about 1800 m.
_Size and Proportions._--Frogs of the genus _Osteocephalus_ are moderate to large hylids. The largest species is _taurinus_, attaining a snout-vent length of 103.1 mm; the smallest is _pearsoni_, which attains a length of 54.7 mm. Considerable intraspecific geographic variation occurs in adult size, especially in _taurinus_. Females of all species attain a noticeably larger size than males, but no significant differences are apparent in proportions (Table 2).
TABLE 2.--Comparison of Size and Proportions in the Species of _Osteocephalus_. (Means are given in parentheses below observed ranges)
======================================================================================================== Species N Snout-vent Tibia Length/ Foot Length/ Head Length/ Head Width/ Tympanum/ Length S-V L S-V L S-V L S-V L Eye -------------------------------------------------------------------------------------------------------- _O. buckleyi_ [M] 30 37.9-48.1 0.478-0.580 0.375-0.444 0.319-0.357 0.329-0.368 0.608-0.820 (43.3) (0.520) (0.408) (0.343) (0.351) (0.711) [F] 31 48.6-75.1 0.476-0.599 0.363-0.469 0.310-0.358 0.318-0.367 0.574-0.905 (61.7) (0.553) (0.428) (0.333) (0.348) (0.734)
_O. leprieurii_ [M] 21 41.2-48.4 0.514-0.571 0.383-0.430 0.308-0.357 0.326-0.368 0.652-0.884 (44.7) (0.538) (0.408) (0.335) (0.348) (0.777) [F] 21 46.6-61.5 0.516-0.592 0.382-0.453 0.314-0.343 0.328-0.363 0.698-0.909 (57.1) (0.539) (0.404) (0.329) (0.349) (0.785)
_O. pearsoni_ [M] 2 45.3-46.2 0.481-0.504 0.404-0.437 0.322-0.335 0.327-0.342 0.660-0.673 (45.8) (0.493) (0.421) (0.329) (0.335) (0.666) [F] 1 54.7 0.521 0.405 0.318 0.346 0.862
_O. taurinus_ [M] 59 40.3-84.6 0.512-0.576 0.387-0.445 0.296-0.345 0.301-0.355 0.638-0.896 (66.3) (0.541) (0.416) (0.318) (0.324) (0.752) [F] 45 45.1-103.1 0.520-0.577 0.391-0.448 0.306-0.334 0.308-0.347 0.640-0.817 (75.8) (0.542) (0.420) (0.321) (0.327) (0.758)