208 
duction which Mr. Gray points out in his paper on the genus Bra- 
dypus: it is much deepened behind, rendering the lower outline 
very convex. And further, there are certain characters pointed out 
by Cuvier in the ‘ Ossemens Fossiles’ which appear to be constant, so 
far as I have been able to observe, as it is only in young specimens 
that the sutures are discernible. They are, first, that in this species, 
the 47 @ collier, the nasal bones are bevelled towards the middle pos- 
teriorly, so that they form a point between the frontals, while in the 
other species they are bevelled in the opposite direction, the frontals 
descending between their extreme points. Secondly, that the pala- 
tine bone forms but a narrow slip within the orbit, and the alisphenoid 
bone occupies a much larger portion of the temporal fossa than in 
the other species. 
The skull spoken of by Mr. Gray as being taken from a skin, pre- 
sents characters intermediate between the other one and that upon 
which the B. affnis is founded, therefore I refrain from inserting the 
latter as a species until further evidences are obtained. 
ArctopitTHecus, Gray. 
Intermaxillary bones short and small; postorbital process slightly 
developed; malar bone with the frontal and zygomatic processes 
slightly marked, or the former wanting, the supratemporal process 
rising obliquely ; pterygoid bones compressed and simple; crota- 
phite impression extending to very near the occipital ridge ; tympa- 
nic bone well-developed, inflated ; lower jaw with its inferior outline 
concave posteriorly, its condyle elevated ; teeth —*, simple, rounded, 
the anterior ones similar, small in the upper jaw. 
A. gcuuaris. Ai a dos brulé. 
A broad patch of soft yellow hair between the shoulders, and a 
black line running through it down the back; the upper anterior 
molars proportionally larger, and the second less, than in the fol- 
lowing species; the occiput again affords us a very good distinction, 
as it is much wider and not so deep as in the following species, and 
the foramen magnum not so large. Two skulls in the British Museum 
present these characters, and evidently belong to adult, probably 
aged, individuals; that of the skeleton, also from Bolivia, seems 
reterable to the other species. 
A. MARMORATUS. 
Fur everywhere more or less lengthened, no yellow spots, dorsal 
line grey brown; anterior upper molars very small, the next rather 
larger than those which follow; occiput deeper and narrower than 
in the preceding species, its foramen larger. 
The A. Blainvillii is not distinguishable by external markings, and 
the skulls bearing that name in the Museum collection all present a 
general robustness, such as age and sex might very probably occasion. 
One of them, which, from retaining some of the sutures, seems to be 
younger than the others, has the frontal bones less swollen, and the 
