1917] 



Stock: Skull and Dentition of Nothrotherium 



143 



Planops, according to Scott, "the premaxillae were evidently large, 

 the facets for them upon the maxillaries being of uncommon size, 

 while the median notch for the spines is a characteristically deep and 

 narrow V." 18 In Megalonyx jeffersoni Leidy describes 1 " the pre- 

 maxillaries as "simple, oblong, quadrilateral plates, a little more than 

 two inches in depth, and three quarters of an inch in breadth." 



Owing to the slenderness of the muzzle, the anterior aspect of the 

 skull of Nothrotherium is decidedly unlike that in Megalonyx. In 

 M. jeffersoni, according to Leidy, "The end of the face is relatively 

 narrower and higher than in Mylodon; and in outline is more ver- 

 tically oblong quadrilateral, with the upper margin convex and the 

 sides nearly vertical."- In Nothrotherium where the first or canini- 



Fijr. 3. Nothrotherium shastense Sinclair. Cranium, no. 208 M. H. S. A., 

 inferior view, X %. Raneho La Brea Beds, California. 



form tooth is absent, the anterior end of the skull is nearly round or 

 oval. The external narial opening is relatively wide transversely as 

 contrasted with the height. The lateral walls show no indication of 

 notching as in Megatherium. With the disappearance of the canini- 

 form tooth in Nothrotherium the depression of the lateral wall of the 

 maxillary anterior to 1VP becomes nearly obsolete. This depression 

 is better developed in Hapalops and is very pronounced in Megalonyx. 



The palate (fig. 3) anterior to may be approximately twice 

 as wide as between the tooth-rows. The lateral borders of the eden- 

 tulous portion of the palate may be nearly straight as in no. 632 or 



is Scott, W. B., Kept. Prin. Univ. Exp. Patag., 1896-1899, vol. 5, p. 322, 1904. 

 io Leidy, J., op. cit., p. 11, 1855. 

 20 Leidy, J., ibid. 



