92 
PATAGONIAN EXPEDITIONS : PALEONTOLOGY. 
available the septum separating the olecranon and coronoid fossae is 
perforated. 
So far as it is possible to make comparison, the radius and ulna (PI. X, 
figs. 9, io, 12) closely resemble the corresponding elements in Megeto- 
therium, and do not call for separate description. The only difference of 
importance appears in the shape of the styloid process of the ulna, which 
is slightly inclined internally, while in Megetotherium it is straighten 
The mutual relationships of the carpal and metacarpal elements is much 
the same as in Protypotherium (cf. Pis. V, fig. 3 ; X, fig. 14) except that 
metacarpal II apparently articulates with the scaphoid. But two specimens 
of the carpus are available for study (Nos.- 9551 and 9481, American Mu- 
seum) and in both of these the proximal end of the second metacarpal 
projects some distance above the magnum, excluding the latter from con- 
tact with the trapezoid. Owing to the partial relief employed in mount- 
ing the only specimen with this portion of the carpus complete (No. 9481 
of the American Museum collection), it is not possible to verify this obser- 
vation by an examination of the articular surfaces of the carpal elements. 
Ameghino (1889, PI. 13, fig. 14) figures a slender pollex in Pactiyruk- 
hos typicus from the Monte Hermoso beds. No trace of a pollex is pre- 
served in the otherwise almost complete fore foot of No. 9481 of the 
American Museum collection, but this cannot be regarded as conclusive, 
as the trapezium is also wanting. The metacarpals decrease in strength 
externally, as in Protypotherium. The third is the longest. Well devel- 
oped keels are present on the distal palmar surfaces. The proximal 
phalanges are slightly arched and taper towards the distal end. The 
proximal articular surface is almost at a right angle to the shaft, is cres- 
centic in outline and slightly concave. Distally, the articulation is c 
to the distal and palmar surface, while the distal articulation of the second 
phalanx is about equally developed on both dorsal and plantar surfaces. 
Distally, the terminal phalanges are flattened transversely and hoof-like, 
without trace of terminal clefts, differing in this respect from Pachyrukhos 
typicus. 
The pelvis (PI. X, figs. 17, 18) is well preserved in one of the specimens 
in the American Museum collection (No. 9242). The gluteal surface 
of the ilium is slightly concave in all dimensions, in contrast with its deep 
concavity in Protypotherium and Inter at herium. Anteriorly, it is obliquely 
truncated from above forward, with prominent anterior and posterior 
