72 



We have three specimens of the animal agreeing with the skulls 

 here described, but they offer no external character by which I can 

 distinguish them from the preceding specimens (A. marmoratus) ; 

 yet the skulls all agree in the greater convexity of the forehead and 

 in the form of the angle of the lower jaw. Two of the lower jaws 

 have a distinct angular ridge up the front symphysis. The figure 

 is taken from the skull of a skeleton received from M. Becker as the 

 B. tridactylus from Brazil. 



It has been suggested that the differences in the form of the hinder 

 part of the lower jaw, which, it should be observed, are not the only, 

 but are the most easily described characters to separate these species, 

 are not sufficient for specific distinction. I am willing to own that 

 it is a fair question of discussion, and one that can only be settled by 

 the comparison of more specimens than we at present possess. Should 

 these variations prove only individual, and not specific, then it must 

 lead us to be very cautious in the formation of species on the exami- 

 nation of skeletons alone, as is of necessity the case m the animals now 

 only found in a fossil state. 



b. Fur elongate, very flaccid, whitish; dorsal streak very short, 

 indistinct, only seen where the hair is worn. 



4. Arctopithecus flaccidus. 



{Skull, Mammalia, PI. XI. f. 1, adult; f. I a, young.) 



Pale grey-brown ; back, sides of the back and hinder part white 

 varied, with a short blackish dorsal streak between the shoulders. 

 Skull with a broad rather convex forehead. (3 spec.) 



Ai (seconde), Buffon, Hist. Nat. xiii. 62. 



Jeunes Ais, Buffon, H. N. xiii. t. 5. 



Bradypus tridactylus, Temm. Ann. Gen. Sci. Phys. vi. 51, not 

 Linn. ; Pr. Max. Abhild. Nat. Braz. t. . $ & jun. ; Beitr. zur 

 Nat. ii. 482. 



B. tridactylus, var. a. $ ?, Desm., and var. d. (J, Mamm. 



Var. 1 . White grey-brown ; back of the hairs blackish, with a short 

 black streak, and with a white spot on each side between the shoulders. 

 (1 spec.) 



Hab. Venezuela ; 3Ir. Dyson. 



Var. 2. Nearly uniform whitish grey-brown ; base of the hairs 

 blackish, without any dorsal streak. (1 spec.) 



Hab. Para ; J. P. G. Smith, Esq. 



This species, of which we have four specimens of different ages in 

 the Museum, is easily known by the length, very loose and flaccid 

 nature of its hair, and the indistinctness of its markings. The black 

 on the back appears to arise from the hair of the shoulders being 

 worn away. Three, of very different ages, are pale grey-brown, 

 with a short, broad, blackish streak between the shoulders, and 

 have the rump and each side of the dorsal streak more or less white, 

 and an indistinct whiteness on the outer side of the upper arms. 



Buffon' s description of his second specimen of ^i?' agrees better with 

 this species than with any other which has come under my observation. 



