1917] 



Stock: Skull and Dentition of Nothrotherium 



159 



injured by rodents, especially toward the occlusal surface. The 

 gnawed surfaces of the tooth do not seem to account entirely for the 

 difference in size of the two ends : that is to say, the tooth narrows 

 toward the occlusal face. This is considered as characteristic of 

 immature individuals. It is apparent also that this tooth is excep- 

 tionally large in comparison with the remaining teeth of Nothrotherium 

 shastense. Furthermore, there are several teeth in the collections from 

 Potter Creek Cave which are not clearly referable to Nothrotherium, 

 but belong perhaps to a small species of Megalonyx. In fact, Sinclair 

 described a specimen, no. 820H, from the cave deposit which he 

 identified tentatively as belonging to Megalonyx wheatleyi. With the 

 fifth superior tooth of M. jeffersoni no. 8497 from Potter Creek Cave 

 agrees in triangular shape but differs in size. The latter specimen 



LP 



Fig. 9. Megalonyx(?), sp. M-, no. 8497, Univ. Calif. Coll. Paine., anterior 

 view with outline of section through pulp-cavity, natural size. Potter Creek 

 Cave, Shasta County, California. 



lacks possibly "the slightly concave" posterior face noted by Leidy 

 in M. jeffersoni, but this can only be regarded as a minor difference. 



In a former note the writer considered specimen 8337 from Potter 

 Creek Cave as probably representing an inferior tooth. The characters 

 • seen in occlusal view relate this specimen much more closely with M 5 

 and Mg than with M- or M-. The concave posterior face in its longi- 

 tudinal extent is a character held in common by no. 8337 and of 

 Nothrotherium from Rancho La Brea. The tooth from Potter Creek 

 Cave differs slightly from the second and third inferior teeth from 

 the asphalt beds in having the four angles of the occlusal surface 

 slightly more sharply defined. 



While the comparatively large size of no. 845)7 is in itself not 

 sufficient reason for generic determination as other than Nothro- 

 therium, in view also of its much closer resemblance to the fifth 

 superior tooth of Megalonyx the identification with the latter is more 

 probable than with Nothrotherium shastense. The fragmentary 



