CACAJAO 305 



(from specimens brought to Paris in 1847 by the Compte de Castel- 

 nau) as a distinct species, under the name of Brachyurus rubicundus. 

 It wholly replaces the white form in the western parts of the Japura 

 delta; that is to say, in a uniform district of country, 150 miles in 

 length, and sixty to eighty in breadth, the eastern half is tenanted 

 exclusively by white Ua):?ris, and the western half by red ones. The 

 district, it may be menti jned, is crossed by several channels, which at 

 the present time doubtless serve as barriers to the dispersal of 

 monkeys, but cannot have done so for many centuries, as the position 

 of low alluvial lands, and the direction of channels in the Amazon 

 Valley, change considerably in the course of a few years. The red- 

 haired Uakari appears to be most frequently found in the forests lying 

 opposite to the mouth of the river which leads to Fonteboa, and ranges 

 thence to the banks of the Uatiparana, the most westerly channel of 

 the Japura, situated near Tunantins. Beyond that point to the west 

 there is no trace of either the red or the white form, nor of any other 

 allied species. Neither do they pass to the eastward of the main 

 mouth of the Japura, nor to the south shore of the Solimoens. How far 

 they range northwards along the banks of the Japura, I could not 

 precisely ascertain ; Senhor Chrysostomo, however, assured me that 

 at 180 miles from the mouth of this river, neither white nor red Uakari 

 is found, but that a third, black-faced and gray-haired species takes 

 their place. 



"I saw two adult individuals of Brachyurus rubicundus at Ega, 

 and a young one at Fonteboa ; but was unable to obtain specimens 

 myself, as the forests were inundated at the time I visited their 

 locality. I was surprised to find the hair of this young animal much 

 paler in colour than that of the adults, it being of a sandy and not of a 

 brownish-red hue, and consequently did not dififer very much from 

 that of the white species; the two forms, therefore, are less distinct 

 from each other in their young than in their adult states. The fact 

 of the range of these singular monkeys being so curiously limited as 

 here described, cannot be said to be established until the country lying 

 between the northern shore of the Solimoens and New Granada be 

 well explored, but there can be no doubt of the separation of the two 

 forms in the Delta lands of the Japura, and this is a most instructive 

 fact in the geographical distribution of animals." 



Cacajao melanocephalus (E. GeoiFroy). 



Pithecia melanocephala Geoff., Ann. Mus. Hist. Nat. Paris, XIX, 

 1812, p. 117; Schleg., Mus. Pays-Bas, Simise, 1876, p. 229. 



