1917] Stock: Skull and Dentition of Nothrotherium 157 



Creek Cave in longitudinal curvature. The longitudinally concave, 

 posterior face of no. 10495 and the distinctness of the angles of the 

 occlusal surface relate this specimen much more closely with the 

 second inferior tooth than with either the third or fourth superior 

 teeth. The occlusal surface resembles also that of Mg. No. 10495 is 

 then either a second or third inferior tooth. 



The last inferior tooth, which in Hapalops is more or less cylin- 

 drical in shape, retains the rounded internal side in Nothrotherium. 

 It thus agrees with Megalonyx in differing markedly in shape from 

 either M 3 or M^. This tooth in Megatherium, although smaller and 

 relatively longer anteroposteriorly than and M3-, is essentially of 

 the same shape as the other inferior teeth. The transverse axis 

 of M 5 in Nothrotherium is directed obliquely to the long axis of the 

 tooth-row, thus resembling Hapalops and Megalony.r. On the outer 

 flattened face of this tooth a median vertical groove may be slightly 

 defined as in no. 208, or well defined as in no. 456. In the presence 

 of this groove, Nothrotherium differs from Hapalops and Megalonyx. 

 The outer anterior and posterior corners of are well rounded. The 

 denser layer of dentine is best developed on the inner and posterior 

 sides and least on the outer side. The border of the occlusal surface 

 is least worn at the middle of the inner side and at the postero- 

 external corner. Between the resulting prominences, the border is 

 beveled posteriorly. In Megalonyx the occlusal surface of the corre- 

 sponding tooth is somewhat similarly worn. It is described by Leidy 

 as having "... a transverse valley, whose boundaries are most 

 prominent at the antero-internal and postero-external angles." 32 



EE VIEW OF SPECIES 

 In a former note 33 the writer briefly described a single skull of 

 Nothrotherium without mandible from Rancho La Brea, which was 

 referred to a new species, N. graciliceps. At that time the only other 

 material of this genus available from the asphalt was a single tooth, 

 no. 10435, in the palaeontological collections of the University of 

 California. In a comparison of the Rancho La Brea N othrotherium 

 with N . shastense from Potter Creek Cave, it was inferred that the 

 lower jaw in the former species was longer than in the latter. The 

 principal difference, however, between the two forms was thought to 

 rest in the shape of the last superior tooth. 



32 Leidy, J., op. cit., p. ] 9. 



-"■Univ. Calif. Publ. Bull. Dept. Geol., vol. 7, pp. 341-358, 1913. 



