EDENTATA OF THE SANTA CRUZ BEDS. 195 



carpal III of Megalonyx and that of Nothrotherium, longer and more 

 slender than in the former, shorter and heavier than in the latter; the 

 distal end bears a narrow trochlea, with immensely developed keel. 



Metacarpal IV is the longest of the series and relatively much longer 

 than in any of the Pleistocene genera, except Nothrotherium, in which it 

 is even more elongate ; the proximal end is moderately expanded trans- 

 versely and palmo-dorsally, with facets for the unciform and for metacar- 

 pals III and V; the shaft is laterally compressed and slender, of quadrate 

 section, but with convex dorsal surface, not flat or concave as in metacar- 

 pals II and III, with straighter lateral borders than in Megalonyx and 

 without any such dorsal ridge ; the distal end also is narrower than in 

 the latter. 



Metacarpal V also resembles that of Megalonyx, but is relatively longer 

 and lighter ; in length it is inferior only to metacarpal IV and is more 

 slender than any other, with the probable exception of metacarpal I ; the 

 projection from the ulnar side of the proximal end is far less prominent 

 and massive than in Megalonyx ; the proximal end articulates with the 

 unciform by a facet which is oblique and almost lateral, but does not 

 reach the pyramidal ; the shaft is very slender and somewhat curved, with 

 decidedly concave ulnar border, and is of subcircular section ; the distal 

 end is small and club-shaped. 



The phalanges are of similar shape in all of the digits, but with cer- 

 tain modifications in each one ; on the whole, they most resemble those 

 of Megalonyx, while in Nothrotherium they are peculiarly differentiated. 



The proximal phalanx is very short, though relatively longer than in 

 the Pleistocene genera, the length slightly exceeding the width and 

 being much surpassed by the dorso-palmar thickness. In shape this 

 phalanx best agrees with that of Megalonyx, but its proximal end is rela- 

 tively less thickened ; the proximal and distal surfaces are much alike, 

 each having a very deep median groove ; in Nothrotherium these grooves 

 notch the dorsal face much more deeply and are separated only by a nar- 

 row bridge of bone. This phalanx is largest in digit III, smallest in V, 

 and slightly larger in II than in IV. 



The second phalanx is very much longer and narrower than the first and 

 has the proximal end much thicker palmo-dorsally than the distal, though 

 the difference is rather less decided than in Megalonyx; the proximal 

 trochlea has two concave facets, separated by a prominent median ridge, 



