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mens 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 the 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. 
(Lower jaw, Mammalia, Pl. XI. f. 3, adult; f. 4, half-grown.) 
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, asin 4. gularis, 
reaches nearly to the rump, while in 4. flaccidus it is confined to the 
upper part of the back. : 
In ‘Griffith’s Animal Kingdom’ there is a figuie 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 4. marmoratus or A. Blainvillit. 
In the British Museum there is a nearly adult and a young speci- 
men of this species, the hinder part of the lower jaws of which are here 
figured. The specimens agree in all points of external colouring with 
the following species (4. Blainvillii) ; but the form of the lower jaw 
at once separates it both from A. gularis and A. Blainvillii. It may 
be the female of the former, the skull having more alliance to that 
species than to 4. Blainvillit. 
The front of the lower jaw of the older specimen is rather promi- 
nent, while that of the younger individual is truncated and quite de- 
stitute of any convexity or keel, like the adult skull of 4. gularis. 
3. ArcTOPITHECUS BLAINVILLII. 
(Skull, Mammalia, Pl. XI. f. 2.) 
Grey-brown, back and outside of the arms white varied, with an 
elongated narrow streak extending nearly the whole length of the 
back ; the forehead very convex and swollen over the back of the orbit. 
Teeth rather large ; front lower compressed. 
Lower jaw distinctly keeled up the symphysis, and slightly angu- 
larly produced on the front edge. 
B. tridactylus Braziliensis, Blainville, Osteog. t. 2, skeleton ; 3, 
skull partly broken. 
Hab. Tropical America. 
