6 SIMIIDJE. 



It is the subject, however, of considerable variation, the most extreme variety 

 being that in which the general colour of the animal, instead of being black, becomes 

 wholly pale yellow {S. entelloides, Is. Geoff. St.-HiL). It may be observed, however, 

 that, even in these very pale animals, which as in S. hoolock are generally females, 

 the paler colour of the hands and feet can to a certain extent be detected. Between 

 these two well-defined extremes every variety of colour is exhibited by the species, 

 but the characteristic specific markings of the face, hands, and feet are preserved. 



In some individuals the index and middle toes of the foot become united by a 

 web f as in S. s?/ndactt/lus. 



Its voice is perfectly distinct from that of JS. hoolock. 



It appears to be confined to Arracan, Lower Pegu, Tenasserim, and to the 

 Malayan peninsula. 



Hylobates pileatus. Gray. 



E.ylobates pileatus, Gray, Proc. Zool. Soc. 1861, p. 136, pi. xxi. ; Cat. Monkeys and Lemurs, B. M, 



1871, p. 10. 

 Rylohates lar, Blyth, Journ. As. Soc. Beng. vol. xliv. 1875, ex. no. p. 2. 



The individuals of this species are generally distinguished by a black area on 

 the top of the head resembling a cap, and by the chest being almost wholly of the 

 same colour, which, however, in some instances extends on to the throat and belly. 

 The back of the head, the upper surface of the trunk, the limbs, the circumference 

 of the black spot on the crown, are greyish, usually paler in the latter area, all the 

 remaining portions being black. Other specimens are all white, with the exception 

 of the back which is brownish, and the top of the head and the chest which are 

 black ; while some are brownish, with the chest, belly, and sides of the face black, 

 the throat also partaking more or less of the latter colour. In some examples the 

 whole of the under parts are black and the whiskers are white. 



It is a most variable Gibbon, and the circumstance that it is to a certain extent 

 resembled by B. agilis, S. leuciscus, and S. mulleri, in the distribution of their 

 colours, has suggested to the minds of some zoologists, and with a show of 

 probability, that they may all ultimately prove to be referable to one species. 



Inhabits Siam. 



Hylobates leucogenys, Ogilby. 



JJOnle, Tabraca, Hist. Civile et Nat. de Siam, vol. ii. 1771, p. 308. 



Hylobates leucogenys,Og^-{S\iY,VvoQ.ZQ(A. Soc. 1840, p. 20; Blyth, Journ. As. Soc. vol. x. 1841, 

 p. 838; Martin, Nat. Hist. Quadrumana, 1841, p. 445 (plate and %. of skull); Is. Geoff! 

 St.-Hil. Comptes Rendus, 1842, vol. xv. p. 717, Arch, du Mus. vol. ii. 1843, p. 535 ; Schinz* 

 Syn. Mamm. vol. i. 1844, p. 28; Gervais, Hist. Nat. des Mammif. 1854, p. 54; Wagner' 

 Schreber, Saugeth. Suppl. vol. v. 1855, p. 20 ; Gray, Cat. Monkeys and Lemurs, B. 'm. f87o' 

 p. 11. 



This species is entirely black, with the exception of the area below the ears, the 

 cheeks, and the part of the throat immediately behind the chin, which are white. 



