1918] Stock : The Pleistocene Fauna of Hawver Cave 



491 



A second phalanx (figs. 8a, 85), no. 19892, belongs to the second 

 digit of the right anterior foot. It is larger than the average corre- 

 sponding- phalanx of M. ha Ha ni from Rancho La Brea and exceeds 

 in total length the longest specimen from the asphalt. In the cave 

 specimen, as well as in the phalanges from Rancho La Brea, the outer 

 condyle of the distal trochlea is the larger and is separated from the 

 inner condyle by a broad and rather shallow groove. The proximal 

 articulating face in no. 19892 and in the specimens from Rancho La 

 Brea consists of two concave facets separated by a thick median 

 ridge, the outer facet being slightly larger than the inner one. 



No. 21461 is a second phalanx of digit three, right posterior foot. 

 This specimen (figs. 9a, 95) differs from the preceding in being only 

 one-half as large. It is very similar in general shape and size to 

 the corresponding phalanges of Mylodon harlani. The thickened 

 median ridge of the proximal articulating face is not as well defined 

 as in no. 19892. The surface of the lower half of this ridge differs 

 from the Rancho La Brea specimens in being concave. No. 21461 

 differs further from M. harlani in the wider overhanging process of 

 the proximal face. The outer condyle of the distal trochlea, as in no. 

 19892, is the larger and is separated from the inner condyle by a 

 groove which widens below. The surfaces of the distal condyles 

 articulating with the ungual are semicircular in outline. 



MEGALONYX ( ? ) , sp. 



A phalanx, no. 19863, represents one of the second podial series. 

 In size as well as in shape this specimen (figs. 10a, 105) approaches 

 more nearly the corresponding phalanx of Megalonyx than it does 

 that of either Mylodon or Nothrotherium. The element in Mylodon 

 which approaches no. 19863 most closely in structure is the second 

 phalanx, digit two, manus. In both specimens the proximal articu- 

 lating surface consists of two concavities separated by a thick median 

 ridge which widens dorsally and ventrally. In Mylodon, however, 

 the concavities have a greater dorso-ventral extent and the proximal 

 extremity narrows more dorsally than in no. 19863 from Hawver 

 Cave. Both elements are elongate anteroposteriorly with the distal 

 end modified into a trochlea for articulation with the ungual. At 

 the base of the trochlea both dorsally and ventrally the phalanx is 

 not so deeply depressed as is the phalanx of Mylodon. A char- 

 acteristic difference between the two phalanges is exhibited by the 

 median groove of the distal trochlea. In Mylodon this groove is wide 



