I 918 ] Stock: The Pleistocene Fauna of Hawver Cave 



507 



the tibia corresponding to the anterior tuberosity in Hapalops had 

 been flattened down and to the outer side of the outer femoral articu- 

 lating surface. In dorsal view this gives a very even anterior margin 

 to the proximal surface. Judging from Leidy's figure 21 of the tibia 

 of Megalongx jcffersoni that genus differs decidedly from Nothro- 

 therium in the well-developed anterior tuberosity, and in this respect 

 resembles more the genus Hapalops. 



At the proximal end the inner femoral articulating surface is large, 

 subcircular and concave. Its antero-external portion is steeply in- 

 clined to form the inner side of the intercondyloid eminence. The 

 latter spine is relatively not as prominent as in the tibia of Hapalops, 

 but this difference may be due to the greater wear of the speci- 

 men from the cave. The fibular facet at the proximal end is more 

 elongated than in Megalonys. The shaft is thickest toward the 

 medial border and narrows laterally. As indicated by Scott the 

 distal end resembles that of Hapalops. Although prominent the 

 inner malleolus is apparently in its width relatively not as broad as 

 that of Hapalops. On the posterior surface there are two tendinal 

 grooves, the external of which is quite broad while the internal one 

 is much narrower. The articulating surfaces for astragalus and fibula 

 extend obliquely across the distal end from the front backward and 

 inward. The inner and outer surfaces for the astragalus are sep- 

 arated by an obscure ridge, and the distal spine is well developed as 

 in Hapalops. The fibular facet is wide anteriorly and narrows behind. 

 It perhaps does not extend so far up along the outer side of the tibia 

 as in Megalonyx. 



Measurements of Tibia, no. 19965 



Greatest length measured along middle of shaft d318 mm. 



Greatest transverse width of proximal end 186.8 



Least width of shaft 66.5 



Thickness of shaft at middle 44 



Greatest transverse width of distal end 138 



Thickness of distal end 65.3 



a, approximate. 



The fibula of Nothrotherium, no. 19966, greatly resembles that of 

 Hapalops in general shape. In proportion to the size of shaft, the 

 fibula of the Pleistocene genus possesses relatively heavier extremities 

 than that of II. longiceps. Contrasted with Mylodon the fibula of 

 Nothrotherium is very much more slender in the region of the shaft 



21 Leidy, J., op. cit., pi. 11, fig. 4. 



