Zoological Society. 351 



backwards or bent a little upwards ; pterygoid bones inflated ; 

 crotaphite impression approaching near to the occipital ridge ; tym- 

 panic bone reduced to a simple ring; lower jaw produced ante- 

 riorly, straight below, its condyle depressed; teeth ^, simple, 

 rounded, the anterior ones in each jaw enlarged, trigonal. 

 C, didactyhis. 



Bradypus, Gray. 



Intermaxillary bones reduced or wanting; postorbital process 

 slightly developed ; malar bone with the frontal and zygomatic pro- 

 cesses sUghtly marked, the supratemporal process rising obliquely ; 

 pterygoid bones inflated ; crotaphite impression terminating at a con- 

 siderable distance from the occiput ; tympanic bone well-developed, 

 forming a bulla ; lower jaw with a flattened square process in front, 

 deep posteriorly, the lower outline convex, the condyle elevated ; 

 teeth j^, simple, rounded, the anterior ones similar, small in the 

 upper jaw. 



B. crinitiis. 



In addition to the character of the pterygoids, which, in the absence 

 of actual knowledge, might possibly have belonged to age or sex, I 

 find this species to be clearly distinguishable from those of the next 

 genus by the great distance that intervenes between the posterior 

 termination of the temporal fossae and the occiput, which is much 

 greater in the old specimens even than in the young of the genus Arc- 

 topithecus. The occiput also differs from them in being proportionally 

 smaller, of a rounder form ; the digastric fossae converging a little 

 superiorly, instead of diverging as in the other genus. The lower 

 jaw also presents a character more decided than the anterior pro- 

 duction which Mr. Gray points out in his paper on the genus Bra- 

 dijpus : it is much deepened behmd, 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 Ai a 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 aUsphenoid 

 bone occupies a much larger portion of the temporal fossa than iu 

 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. affinis is founded, therefore I refrain from inserting the 

 latter as a species until further evidences are obtained. 



Arctopithecus, Gray. 



Intermaxillary bones short and small ; postorbital process slightly 

 developed ; malar bone with the frontal and zygomatic processei 



