EDENTATA OF THE SANTA CRUZ BEDS. 341 



Aside from the unguals, the phalanges do not differ markedly from 

 those of Hapalops and have little resemblance to the highly specialized 

 phalanges of Megatherium. The first phalanx of digit I is elongate and 

 slender ; the proximal trochlea is moderately grooved and deeply notched 

 on the palmar border for the metacarpal carina, and the distal trochlea is 

 also grooved and somewhat asymmetrical. In the second digit this 

 phalanx is much like that of Hapalops in shape, but is relatively a little 

 longer and its proximal end is somewhat less deeply grooved. The 

 second phalanx of digit II differs but slightly from that of Hapalops, 

 except in being a little shorter; the proximal trochlea is less deeply con- 

 cave and its median dorsal portion does not form so prominent a beak; 

 the distal trochlea has a shallower median groove and is invaded in the 

 median dorsal line by a broad, shallow sulcus, which is not present in 

 Hapalops, but there is no such fossa on the dorsum of the shaft, for the 

 beak of the ungual, as appears in that genus. In digit III the second 

 phalanx is shorter but much stouter than in digit II ; it differs consider- 

 ably in form from that of Hapalops, the median ridge and dorsal beak of 

 the proximal trochlea are much less pronounced, and the phalanx is not 

 constricted palmo-dorsally below the proximal trochlea ; the distal trochlea 

 has a shallower median groove. 



The unguals are very different from any known Santa Cruz genus of 

 the MegalonychidcB and have considerable likeness to those of Mylodon. 

 Compared with that of Hapalops, the ungual of digit II is very long, 

 broad and low ; its dorso-palmar diameter is much less and consequently 

 the dorsal surface is much less strongly arched, while the ventral surface 

 is more so ; the proximal trochlea is broader and less concave and has a 

 far less prominent intercondylar ridge ; the subungual process is extremely 

 large and heavy ; the distal end is bluntly rounded and the cleft becomes 

 a very shallow dorsal groove. In the pollex the ungual is similar, but 

 very much shorter and less depressed. 



In the following table the lengths of the fore-limb bones are only ap- 

 proximate, but the error must be slight. 



MEASUREMENTS. 



Humerus, length 309 Radius, proximal width 035 



" proximal width 090 " " thickness 033 



thickness 063 " distal width 052 



Radius, length 303 " " thickness 038 



