574 BidTetin American Museum of Natural History. [Vol. XIX, 



without the encroaching ridge which bounds the articular sur- 

 face in that genus. The convex surface of each condyle is 

 inclined a little outwards ; the inner edges bounding the fora- 

 men magnum converge from the upper to the lower boundary. 

 The condyles stand away from the skull more than in Mylodon, 

 and the greater articular area is on the lower surface. The 

 foramen magnum looks downwards as well as backwards. 



The tympanic is lost, leaving exposed the petrous bone 

 wedged in between the sphenoid, exoccipital, and squamoso- 

 temporal bones. The inner portion is a subcompressed, 

 conical protuberance uniting with the basisphenoid in a 

 straight line, forming the outer and posterior margin of the 

 carotid canal. In Mylodon the basisphenoid is distinctly 

 emarginated for its reception. On the outside and posterior 

 to the conical process the petroso-temporal sends down a 

 rugged process forming the anterior boundary of the jugular 

 foramen and the depressions for the stylohyal. In front it 

 bounds the posterior part of the tympanic cavity. The bony 

 canal of the Eustachian tube expands where it communicates 

 with the narial aperture, separating the pterygoids from the 

 sphenoid protuberances. 



Side View. — As in Mylodon the side view of the skull 

 presents the form of an elongated parallelogram. The occipi- 

 tal plane inclines forward as it rises to the upper surface of 

 the skull. The top of the cranium presents a nearly straight 

 line slightly depressed at the posterior end of the nasals. The 

 muzzle ends in a slightly curved line; nasals and maxillaries 

 about the same length above, with protruding palate. Ven- 

 trally the basicranial outline is interrupted by the greatly 

 expanded pterygoid. 



The supraoccipital element forms nearly the whole of the 

 posterior region of the skull, joining the parietals in a trans- 

 verse lambdoidal suture, which forms the crest but does not 

 encroach upon the coronal surface of the skull. From the 

 condyles the broad occipital plate rises upward and forward, 

 first at an angle of about 75° to two-thirds its height, and then 

 forward to the lambdoidal suture at an angle of 60°. It is 

 divided into two equal areas by a prominent occipital crest. 



