Sinclair: typotheria of the santa cruz beds. 
29 
toward the palmar margin. It is irregularly triangular in outline, slightly 
convex in dorso-palmar section and strongly concave transversely. The 
trapezoidal surface is narrow and broadly convex in dorso-palmar section, 
while the facet for the scaphoid is concave from side to side and also 
dorso-palmarly. The lunar surface is sigmoid in the latter direction, 
slightly convex palmarly, and concave dorsally. It is confluent dorsally 
and externally with the irregularly triangular, plane facet for the unciform. 
The metacarpal facet is quadrangular in outline and deeply concave in 
dorso-palmar section, while transversely it is plane. The unciform is a^ 
large element, irregularly tetrahedral in form, supporting proximally a 
large, transversely sigmoid surface for the cuneiform and proximo-inter- 
nally a concave semicircular facet for the lunar. Internally, there is a large 
surface, slightly concave proximo-distally, for the third metacarpal and the 
magnum. Distally, there are two surfaces for the fourth and fifth metacar- 
pals respectively. That for the former is triangular and concave in all 
dimensions, while the surface for metacarpal V is oval, concave in dorso- 
palmar section and slightly convex transversely. Proximally, the meta- 
carpus is strongly interlocking. The articular surfaces are sufficiently well 
shown in the figure (PI. V, fig. 9) to make detailed description unneces- 
sary. The shafts are transversely flattened and bear well marked plantar 
keels, distally. The distal articular surfaces of the proximal phalanges 
are confined to the distal and palmar surfaces, while the proximal surfaces of 
the second row present upward and forward, indicating a moderate amount 
of angularity in the position of these elements (see restoration of the 
skeleton, PI. VII). The ungual phalanges are laterally compressed hoofs, 
with slight, more or less well defined terminal clefts. All the digits sup- 
ported terminal phalanges, but in none of the specimens studied has the 
terminal phalanx of digit V been preserved. 
The ilia (PI. VI, figs. 9, 10) are broadly expanded, with deeply concave 
gluteal fossae and prominent anterior superior and posterior inferior spines. 
Between the anterior and posterior superior spines the crest of the ilium 
is inclined forward obliquely. Inferiorly, the iliac margin is broad, flat- 
tened and channeled longitudinally by a shallow groove. The neck is 
stout and the tubercle for the rectus femoris rather prominent and rugose. 
Ilio-pectineal eminences are practically absent. The ischium is broadly 
expanded posteriorly, with prominent spine and tuberosity. The ischial 
ramus and the pubis are slender. 
