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). {152}_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). CHARACTERS.--Face black; colour entirely black, but becoming brown on the back and sides, and with a white superciliary band, and sometimes ashy-grey cheeks. This is the typical form of the species in Mid-Sumatra, where the present writer had the opportunity of examining it alive. It was with difficulty distinguished from _H. syndactylus_, except from its size and the presence of the white superciliary band. Other specimens (but none of them met with to the south of the Moesi river by the present writer) have been described, with the occiput, the back from immediately behind the shoulders, the flanks, the hips, and the outer surfaces of the fore- and hind-limbs, pale yellow. The shoulders, chest, and belly, and the inside of the limbs and feet dark brown; eyebrows and whiskers pale grey. (_Anderson._) The variety described as _H. pileatus_ is distinguished by a black cap-like patch on the top of the head; the chest, throat, and belly black; the back of the head, the upper surface of the body, the limbs and area round the black cap grey. This variety may also be entirely white, except for the coronal cap {153}and chest being black, and the back brown; or the pervading colour may be brown, the sides of the face and the under surface black, and the whiskers white. The index and middle fingers are occasionally webbed together. All the hairs on the arm and fore-arm converge towards the wrist.