28 
PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
distally concave facet on the outer side of the process in contact with the 
magnum. Internally, the palmar surface supports a heavy rugose tuber- 
cle. The lunar is a large element, wedge-shaped in dorsal view, with a 
broad, strongly convex proximal surface for the radius. Distally, it is in 
contact with the magnum and unciform. The surface for the former is 
divided into two portions, a small dorsal convex area, wedge-shaped in 
outline, and a large, irregularly quadrangular palmar tract, strongly concave 
in dorso-palmar section. The unciform facet is triangular, slightly con- 
cave, and but little differentiated from the surface for the cuneiform. In- 
ternally and distally, there is a small triangular concave facet for the scaph- 
oid. Externally, contact with the cuneiform is secured by a broad sur- 
face of irregular outline, concave in dorso-palmar section and convex 
proximo-distally. The cuneiform is broadly grooved proximally for the 
styloid process of the ulna. On the palmar surface is a large oval flat 
facet for the pisiform, distally an oval concave facet for the unciform and 
internally a small, crescentic, convex surface for the lunar. Externally, the 
cuneiform supports a large protuberance almost half as large as the bone 
itself. The pisiform is a large T-shaped element, the cross bar of the T 
articulating with the cuneiform. The shaft is quite heavy, broadly convex 
in cross-section dorsally and more sharply angulate on the palmar surface. 
Distally, the shaft is expanded and is either abruptly truncate (P. australe ) 
or terminates in a broad convexity [P. prczrutilum). The trapezium is 
convex internally and slightly rugose, with no trace of an articular surface 
for the pollex. Externally, it articulates with the second metacarpal, which 
is deeply excavated for its reception, while proximally it is in contact, by 
a small triangular facet, with the trapezoid. The latter is a triangular ele- 
ment, broad dorsally, but tapering toward the palmar margin, where it 
supports a heavy tubercle. Proximally, there is a triangular facet for the 
scaphoid, concave in dorso-palmar section and slightly convex transversely, 
and, distally, a similar facet convex in both dimensions for the second 
metacarpal. Internally, there is slight lateral contact with the trapezium, 
while externally and distally the surface for the magnum is but little dif- 
ferentiated from the metacarpal facet. The magnum is narrow dorsally, 
but increases in proximo-distal diameter toward the palmar margin. It 
is in contact with the second metacarpal, the trapezoid, the scaphoid, the 
lunar and the unciform, and distally rests upon the third metacarpal. The 
surface for the second metacarpal is narrow dorsally, but increases in width 
