142 University of California Publications in Geology [ Vol.10 



In Megalonyx the zygomatic process of the squamosal is much 

 heavier than in Nothrotherium. In M. leidyi 15 and in Megatherium 

 american um ie this process has completely fused with the malar. The 

 postorhital border of the malar is decidedly more curved in M. leidyi 

 than in Nothrotherium. The ventral prong is also relatively more 

 slender at the base in M. leidyi. 



The parietal sends downward and forward a narrow extension 

 which usually meets the lateral portion of the alisphenoid. Occasion- 

 ally this extension docs not reach the alisphenoid but is interrupted 

 by the frontal. The foramen rotundum and foramen ovale open 

 together as in Hapalops and may form a slightly larger orifice than the 

 foramen lacerum anterius. The orbitosphenoid is not clearly defined 

 by suture. The optic foramen lies at the posterior end of a groove 

 which widens anteriorly, and may lie somewhat obscured by the over- 

 hanging of the frontal. 



The premaxillaries, although originally present in the Rancho La 

 Brea skidls. have not been thus far recognized in the collections. 

 Their articulating surfaces on the maxillaries reveal some interesting 

 peculiarities. On each side of the small median V-shaped notch the 

 maxillary is thickened, especially the palatal portion. This thickening 

 of the maxillary extends well up along the sides of the external narial 

 opening, in some skulls reaching nearly halfway to the top of the 

 orifice. In the Brazilian species described by Reinhardt, the pre- 

 maxillary is shown as a Y-shaped element. In Reinhardt 's figure 17 

 the median arm of the posterior end is seen to be short, while the 

 lateral arm is longer and appears to curve upward. This apparently 

 corresponds with the thickening of the maxillary at the inferior 

 external angle of the narial opening. The anterior arm of the pre- 

 maxillary was presumably not very long in the Nothrotherium from 

 the asphalt beds. 



In Hapalops a similar Y-shaped premaxillary is present. The 

 articulation of this element with the maxillary may somewhat resemble 

 that in the Rancho La Brea genus. The articulation between pre- 

 maxillary and the end of the palatal portion of the maxillary is not as 

 extensive in Nothrotherium as in Hyperieptus. In the Miocene 



is Lindahl, J., Description of a skull of Megalonyx leidyi, n.sp., Trans. Amer. 

 Philos. Soc, vol. 17, n.s., pp. 4-6, pi. 1, 1893. 



1,1 Owen, R., On the Megatherium (Megatherium americanum, Cuvier and 

 Blumenbach), Ft. 3, The skull, Philos. Trans. Roy. Soc. Lond., vol. 146, pi. 21, 

 fig. 1, 1856. 



it Reinhardt, J., op. tit., pi. 1, fig. 3, 1878. 



