1918] 



Stock: The Pleistocene Fauna of Haivver Cave 



503 



prominent as in the humerus of Megalonyx from the asphalt beds. 

 The inner and outer tuberosities of the proximal end are separated 

 from the head by well-defined grooves. Anterior to the middle of 

 the head the tuberosities are connected by a relatively broader shelf 

 than in M. jeffersoni. On the anterior face of the inner tuberosity 

 is a deep groove which extends parallel to the shallow bicipital groove. 

 This channel is lacking in the humerus of Megalonyx. There is no 

 deep groove in the humerus of Hapalops available for comparison, but 

 in this specimen a broad, shallow groove or depression extends 

 obliquely downward and across the anterior surface of the internal 

 tuberosity from its upper border. 



The pectoral ridge is distinct along the greater part of the shaft, 

 forming the antero-internal border above the middle of the humerus. 

 In the Miocene genus Hapalops this ridge extends along the middle 

 of the shaft. The eminence formed by the union of the pectoral 

 and deltoid ridges is of much less height in the Hawver Cave specimen 

 than in Megalonyx. In Hapalops the elevation of the distal end 

 of the pectoral ridge is very pronounced. An entepicondylar for- 

 amen is present as in Megalonyx and in Hapalops. The ulnar portion 

 of the distal trochlea resembles Mylodon and differs from Megalonyx 

 in being approximately flat transversely and in sloping downward 

 and inward from the middle of the trochlea, reaching slightly below 

 the level of the radial portion. It is, however, distinctly convex 

 anteroposteriorly as in Megalonyx. 



Measurements of Humerus, no. 10631 



Greatest length 444. mm. 



Width at tuberosities a97 



Least width of shaft a45.5 



Greatest width of distal expansion «170 



Width of distal trochlea 95.3 



«, approximate. 



An unciform, no. 22899, is nearly complete, lacking only the 

 dorso-external portion which has been broken away. This has de- 

 stroyed the greater part of the facet for metatarsal 5 as well as some 

 of the cuneiform surface, but the remaining facets are well preserved. 



When viewed from the proximal end (fig. 25c) the unciform 

 of N othrotherium approaches that of Hapalops rather more closely 

 than does the unciform of Megalonyx in the expanse of bone at 

 the ventro-external angle. The cuneiform surface does not form 



