338 PATAGONIAN EXPEDITIONS'. PALAEONTOLOGY. 



Although none of the fore-limb bones is complete, they are all so 

 nearly so that a close approximation of their length may be obtained. 

 With many resemblances to those of the contemporary Megalonychidcz, 

 these bones have also a suggestive likeness to those of Megatherium, 

 especially in their length and slenderness as compared with those of the 

 hind-limb. The following table will show the very marked contrast 

 between the present species and Hapalops longiceps in this respect, and 

 the likeness of the former to Megatherium. In each species the length of 

 the femur is taken as 100 and the other bones are calculated in percentages 



of that length. 



MEASUREMENTS. 



Hapalops longiceps. P. potens. Megatherium. 



Femur 100 100 100 



Humerus 90.3 103.6 105.3 



Radius 80. 1 101.6 94.6 



Ulna 92.9 1 1 5.4 106.6 



Tibia 9.17 81.1 84 



The humerus displays a general likeness to that of Hapalops, with a 

 number of minor differences; the tuberosities are much larger than in 

 Megatherium and as prominent as in Hapalops, though of more equal 

 size, the external one being larger and the internal one smaller. The 

 shaft is proximally broad and antero-posteriorly compressed, narrowing 

 downward to a point just above the distal expansion ; the deltoid area is 

 less prominent than in the large species of the latter, but far longer, 

 extending down the shaft below the level of the epicondylar foramen, 

 where it abruptly terminates ; the epicondylar foramen is covered by an 

 unusually narrow bridge and from the course of this bridge it may be 

 inferred that the epicondyle was less developed than in Hapalops. No 

 part of the supinator ridge remains, but enough of the shaft is preserved 

 to show that the ridge had no such proximal extension as in the last 

 named genus. The humerus of Megatherium is very characteristic in 

 appearance, which is chiefly due to the great reduction of the tuberosities 

 and deltoid area, the slender, cylindrical proximal part of the shaft, the 

 immense breadth distally, and the loss of the epicondylar foramen. 



The radius resembles that of Megatherium in shape and in its remark- 

 able elongation, being, in fact, longer in relation to both the humerus and 

 the femur; the head is discoidal, not transversely oval, as it is in the 



