508 University of California Publications in Geology [Vol. 10 



and is relatively much longer. The proximal expansion has its 

 greatest diameter anteroposterior^ and hears along the inner side 

 of the upper surface a tibial facet. At the posterior end of the 

 proximal extremity and on the dorsal surface adjacent to the tibial 

 facet is a small articulating surface. This facet apparently indicates 

 the presence of a fabella along the outer side of the femur. In the 

 second specimen, no. 19857, from Hawver Cave, representing only 

 the proximal end of a fibula, this facet is lacking. The tibial side of 

 the shaft is flattened while the remaining surface of this portion of 

 the fibula is convex with the development of a rugose area along 

 approximately the middle. The distal extremity is roughly pyra- 

 midal in shape with transverse diameter greater than the antero- 

 posterior diameter. 



Measurements of Fibula, no. 19966 



Length a286.2 mm 



Greatest anteroposterior diameter of proximal end 75.5 



Transverse diameter of proximal end a65 



Anteroposterior diameter at middle of shaft 24 



Transverse diameter at middle of shaft 23.9 



Anteroposterior diameter of distal end 59.6 



Greatest transverse diameter of distal end o92 



a, approximate. 



The astragalus of Nothrotherium resembles that of Megatherium 

 in its shortness and the shape of the inner portion of the articulating 

 surface for the tibia, but it is much smaller in the former genus. 

 This element (figs. 28a, 28&) is apparently less like the corresponding 

 structure of Hapalops in shape than is that of Megalonyx. The 

 angle between the inner and outer divisions of the tibial surface is 

 more distinct than in the astragalus of the Brazilian species described 

 by Reinhardt, as well as in Hapalops and Megalonyx. Distally the 

 two divisions of the tibial surface are separated by a deep, V-shaped 

 notch as in Reinhardt 's form. The fibular surface in the Hawver 

 Cave specimen is relatively higher and not as long as in the Miocene 

 genus. The articulating face for the fibula is less sharply separated 

 from the tibial surface, especially in the distal region, where it grad- 

 ually slopes downward to the calcaneal border. 



The narrow and concave external calcaneal facet in the Hawver 

 Cave specimen is more as in Hapalops than in Megalonyx. The distal 

 half of this surface is deepened into a broad concavity sinking in- 

 ternally into the interarticular channel which obliquely traverses the 



