1903.] Brown, A Netv Genus of Ground Sloth. 577 



curved line from the lachrymal foramen to the middle of the 

 muzzle, there is a line of foramina of decreasing size. 



Top View. — The length of the skull from the condyles to 

 the upper anterior border of the maxillary is about the same 

 as in the type of M. robustus. In the mastoid region it is 

 slightly narrower, while across the anterior end of the zygoma 

 at its widest point, behind the postorbital process and at the 

 muzzle, it is much narrower. The upper surface is uniformly 

 smooth; gently convex transversely ; nearly flat in the parie- 

 tal region, and slightly depressed from the postorbital process 

 forward, but much less than in Mylodon. The face is much 

 narrower than in M. robustus and the nasals are more highly 

 arched; in the type, the nasals are crushed down into the 

 narial opening. At the anterior end the nasals are slightly 

 deflected, terminating in an outer rounded edge, the median 

 halves presenting wide notches with two central, extended 

 points and articular upper faces, to which were probably 

 attached an incipient osseous interseptum. No well defined 

 ridge separates the top of the skull from the temporal fossa, 

 this surface merging into the sloping sides of the skull with- 

 out any marked separation. The posterior boundary is 

 formed by the thickened deltoid ridge, behind which are seen 

 the sloping occipital region and the condyles. 



Lower Jaw. 



Dentition. — The first molar is smallest in diameter and 

 simplest of the series : it is ellipsoid in cross-section and tapers 

 to a point, the internal and posterior borders of which are worn 

 down, leaving a crescentic anterior border. This tooth pro- 

 jects far above the crowns of the succeeding teeth (canine- 

 like) and has no opposing tooth in the upper jaw. 



The second molar presents an irregular trapezoidal outline 

 with rounded angles, the posterior one most produced. The 

 external side is convex, while the internal side is strongly 

 concave, the concavity marked by a deep sulcus in the middle. 

 The anterior and the posterior sides are concave, the latter 

 more strongly pronounced. The sulci of the internal and the 



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