140 University of California Publications in Geology [Vol. 10 



Nothrotherium differs from Megalonyx and agrees with Hapalops 

 in the long and slender muzzle (fig. 1). In no. 632 10 the anterior ends 

 of the maxillaries are noticeably flared. This character is less appar- 

 ent in no. 633 and may be but little developed as in no. 634. The 

 nasals are long and may be more decidedly arched in some skulls than 

 in others. In no. 632 the fronto-nasal suture is convex posteriorly, 

 thus resembling most species of Hapalops. This suture may, however, 

 vary in Nothrotherium. It may be decidedly V-shaped as in no. 633, 

 but in this specimen the original suture appears to have been some- 

 what in advance of the present separation. In no. 633 the nasals 

 have apparently fused with the frontals, a secondary or pseudo fronto- 

 nasal suture developing posterior to the original suture. A similar 

 abnormality in the separation between nasal and frontal has been 

 noted in skulls of Mylodon harlani from Rancho La Brea. 11 



In some specimens the lachrymal is not as prominent in superior 

 view as in species of Hapalops, but its canal is very much in evidence. 

 In Megalonyx the lachrymal and its canal are apparently not to be 

 seen in dorsal aspect. The postorbital processes of the frontals may 

 be very blunt in some specimens of Nothrotherium, thus being more 

 as in Megalonyx and differing from Megatherium. Between and 

 slightly posterior to the supraorbital borders, the frontals sag in the 

 middle line. This sag is perhaps most evident in the largest specimen, 

 no. 634. and in skull 203. In skull 15 it is practically absent. 



The temporal ridges are but faintly marked in all specimens from 

 Rancho La Brea. Nothrotherium thus resembling the Miocene Mega- 

 lonychidae. At the coronal suture where the crests approach each 

 other most closely, the distance between them may vary. There is 

 never a pronounced sagittal or lambdoidal crest present as in Mega- 

 lonyx. In front of the weak lambdoidal crest the dorso-lateral surface 

 of the parietal may sag slightly. This sag is distinctly developed in 

 no. 633 where it reaches the median dorsal suture of the cranium, or 

 it is hardly discernible, as in skulls 632 and 634. In all skulls of 

 Nothrotherium the supraoccipital is more prominent in superior view 

 than in Megalonyx. It is very evident in skull 208 (fig. 1). 



As indicated in a former paper, 12 the Brazilian species described 



10 All numbers used in the following comparisons in this paper, unless other- 

 wise stated, are the catalogue numbers of specimens in the Museum of History, 

 Science and Art of Los Angeles. 



11 Stock, C, Skull and dentition of the Mylodont sloths of Eancho La Brea, 

 t T niv. Calif. Publ. Bull. Dept. Geol., vol. 8, p. 322, 1914. 



is Stock C, Univ. Calif. Publ. Bull. Dept. Geol., vol. 7, p. 343, 1913. 



