56 
PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
flattened. Its anterior margin terminates in a sharp flange similar to that 
described in Protypotherium. At the level of the radial tubercle the shaft 
is antero-posteriorly expanded, but rapidly decreases in width distally. 
The styloid process is long, with a globular head. The radial articular 
surface is oval in outline and plane. 
The manus (PI. VIII, fig. i) is tetradactyl. A pentadactyl manus, here 
reproduced as text figure io, A, with large opposable thumb and sepa- 
rate os centrale is referred by Ameghino (1891$, p. 394, fig. 96) to Inter- 
atherium (fcochilus) robustum. No manus of Interatherium in the Prince- 
ton or American Museum collections has more than four digits and 
B 
Fig. io. 
A, Right manus with opposable pollex and separate centrale, x f. B, Right pes with oppos- 
able hallux, x I (after Ameghino). Both have been referred erroneously to Interatherium rob?istum. 
neither in Interatherium nor in any of the Santa Cruz Typotheria does 
the centrale occur as a separate element. In shape and arrangement, 
there is the closest similarity between the carpal elements of Interatherium 
and Protypotherium. Some slight differences in the shape of the various 
articular surfaces are noticeable. The proximal surface of the scaphoid 
is deeply excavated antero-posteriorly in contrast with its even convexity 
in Protypotherium. On the lunar the facets for the unciform and cunei- 
form are wedge-shaped in outline and differentiated from each other, 
unlike Protypotherium. The cuneiform does not differ greatly from the 
corresponding element in ProtypotJierium. The ulnar surface is continued 
externally over the neck of the prominent external tubercle. The trape- 
zium is a small element, laterally compressed proximally, with surfaces for 
