The Gibbons are confined to two Sub regions of the Indian Region. With the exception of the Siamang, all the so-called species of Hylobates are so closely allied to each other, and differ by characters of such slight importance, that they seem to be hardly worthy of specific distinction. (Thomas.)
I. THE AGILE GIBBON. HYLOBATES AGILIS.
Pithecus lar (nec L.), Geoffr., Ann. Mus., xix., p. 88 (1812).
Hylobates agilis, F. Cuv., Hist. Nat. des Mammif., Sept. 1821, pls. v., vi.; Müller, Tijdschr. Nat. Gesch., ii., p. 326 (1835); Martin, Mammif. Anim., p. 416 (1841); Fry, P. Z. S., 1846, p. 11; Gray, Cat. Monkeys Brit. Mus., p. 12 (1870); Schl., Mus. Pays-Bas, vii., p. 17 (1876); Anderson, Zool. Res. Exped. Yun-nan, p. 9 (1878; with full synonymy).
Pithecus agilis, Desmar., Mamm., p. 532 (1820).
Simia lar (nec L.), Raffl., Tr. Linn. Soc., xiii., p. 242 (1822).
Hylobates lar (nec L.), F. Cuv., Hist. Nat., Mamm., pls. 7, 8 (1824); Blyth, J. A. S. Beng., xliv., ex. no., p. 2 (1875).
Hylobates variegatus, Temm., Monogr. Mamm., i., p. xiii. (1827); Wagner in Schreb. Säugeth. Suppl. v., p 16 (1855); H. O. Forbes, Nat. Wand. East. Arch., p. 156 (1885).
Hylobates rafflesii, Is. Geoffr., Cat. Méth. Primates, p. 8 (1851); Gray, Cat. Monkeys Brit. Mus., p. 11 (1870).
Hylobates pileatus, Gray, P. Z. S., 1861, p. 136, pl. xxi.; id., Cat. Monkeys Brit. Mus., p. 10 (1871); Anderson, Zool. Res. Exped. Yun-nan, p. 6 (1878).