Zoological Society. 231 



A. tridactylus, var. Cuvier, Oss. Foss. v. t. 5. f. 1, 2, 3, skull ; cop. 

 Cuv. R. A. Ed. Illust. t. 70. f. 1 a. 



B. tridactylus /3, Fischer, Syn. 387- 

 Hab. Bolivia, Bridges ; Guiana, RuppelL 



This species was well-described by Buffon, and is at once known by 

 its dark colour, white varied back, and the yellow patch of soft hair 

 between the shoulders. 



Cuvier states (Reg. Anim. ed. 2) that M. Temminck thought that 

 the yellow spot on the back depended on the skin being worn in that 

 part. Probably he never saw a specimen, or he could hardly have 

 made such an observation. 



According to Mr. Waterhouse, Mr. Bridges considers the specimens 

 here described as the males of A. marmoratus, 



Cuvier' s upper figure of the skull (fig. 1) most accurately represents 

 the form of the hinder end of the lower jaw, the other figures being 

 distorted by the perspective position. 



There are two specimens in the Museum collection, one half the 

 size of the other ; the smaller specimen is yellower on the face and 

 much darker on the neck, forming a nearly black collar, and the 

 white is smaller in quantity and more mixed with the grey-brown of 

 (he back. The larger one is probably a male, which according to the 

 observations of the Prince of Wied is whiter than the female. 



2. Arctopithecus marmoratus. 



Grey-brown, back and outer side of the arms white varied, with an 

 elongated narrow streak extending nearly the whole length of the 

 back. 



The angle of the lower jaw longly produced, narrow, subacute. 



B. tridactylus, var. Griffith, A. K. t. 136. 



Bradypus tridactylus Guianensis, Blainv. Osteogr. Brad. t. 3. 



Hab. Brazils ; Gordon Graham, Esq. 



This species, which is the most common in English collections, is 

 easily known by the whiteness of the back and limbs, which is well- 

 defined from the uniform dark grey-brown tint of the rest of the body ; 

 the dorsal streak is always very distinctly marked, and, as in A. gularis, 

 reaches nearly to the rump, while in A.Jlaccidus it is confined to the 

 upper part of the back. 



In ' Griffith's Animal Kingdom ' there is a figure by T. Landseer of 

 this species, taken from an adult specimen in spirits in the British 

 Museum, which appears to have formed part of Sir H. Sloane's col- 

 lection ; but the character of the colouring of the back is not well- 

 shown, and it may represent either A. marmoratus or A. Blainvillii. 



In the British Museum there is a nearly adult and a young speci- 

 men of this species. The specimens agree in all points of external 

 colouring with the following species {A. Blainvillii) ; but the form of 

 the lower jaw at once separates it both from A. gularis and A. Blain- 

 villii. It may be the female of the former, the skull having more al- 

 liance to that species than to A. Blainvillii. 



The front of the lower jaw of the older specimen is rather promi- 



