1917 



Stock: Skull and Dentition of Nothrotherium 



147 



hyal process is a deep groove which reaches the occiput and extends 

 for a short way along its lateral border. The position of the occipital 

 condyles with reference to the pterygoid bullae has already been 

 noted. The condyles in ventral aspect are not obliquely placed as in 

 Megalonyx, and project posteriorly much less than in that genus or in 

 Megatherium. They may be widely separated as in no. 313, or much 

 closer together as in no. 203. By far the greater articulating surface 

 of the condyles is directed downward, forward and outward. Leidy 

 states that in Megalonyx the articulating surface of the condyles is 

 bent at about the middle. In no. 633 the dorsal portion of the outer 

 border of the condyle is curiously flattened by a rough and rather 

 extensive surface. The foramen magnum may be transversely oval 

 in shape. It opens more downward than in Megalonyx. 



The base of the zygoma is long, and the glenoid fossa is somewhat 

 concave transversely. The zygomatic process is quite like that in 



Fig. 4. Nothrotherium shastense Sinclair. Cranium, no. 208 M. H. S. A., 

 posterior view, X %. Rancho La Brea Beds, California. 



Ha pal ops, differing from Megalonyx in not projecting so far from 

 the side of the skull. 



As in Miocene genera, the occiput of the Rancho La Brea Nothro- 

 therium is nearly vertical or inclined slightly beyond the occipital 

 condyles. The supraoccipital forms usually an extensive, forwardly 

 inclined surface. In posterior view (fig. 4) the condyles are seen to 

 be as a rule more widely separated than in Hapalops. In no. 203 

 their position is more as in the latter genus. The posterior face of the 

 condyles is relatively smaller than in Hapalops. The dorsal lip of the 

 foramen magnum is notched at the middle only in skulls 15 and 166. 

 The median vertical ridge of the occiput does not usually reach the 

 foramen magnum. It is sharp below but greatly broadens dorsally on 

 the surface of the supraoccipital. Where the vertical surface of the 

 occiput meets the forwardly inclined surface a heavy, rugose, trans- 



