SINCLAIR : MARSUPIALIA OF THE SANTA CRUZ BEDS. 353 
posterior side, indicating somewhat greater power of pronation and supi- 
nation. The bicipital tubercle is placed farther toward the outer side of 
the bone than in Thy lacy mis, corresponding rather with its position in 
Sarcophilus , and is much larger than in the former genus, although con- 
siderably smaller than in Prothylacynus. The radial shaft is slightly 
curved and approximately circular in median transverse section, becoming 
oval in cross section toward the distal end, in striking contrast with the 
sharply triangular section of this portion of the bone in Prothylacynus . 
The distal end is much deeper than in the latter genus, with the articular 
surface convex antero-posteriorly, as in Thylacynus , while in Prothylacynus 
it is concave. The styloid process is longer and heavier than in the last- 
named genus. 
The ulna (PL XLV, figs. 2, 2 a) is much shorter and heavier than in 
Thylacynus. The posterior border is broadly concave. In this respect 
Borhycena differs from the other Santa Cruz thylacynes and resembles the 
existing genus. The olecranon is broad and heavy, comprising about 
one fifth the total length of the shaft. Its proximal end is greatly thick- 
ened and rugose. The greater sigmoid cavity is wider and deeper than 
in the recent genus and the coronoid process projects farther forward. In 
the lesser sigmoid cavity, the radial articular surfaces are more broadly 
connected proximally than in either Thylacynus or Prothylacynus. The 
shaft is considerably flattened and broadly grooved on the outer side. 
The distal end is much heavier than in Thylacynus , with large hemi- 
spherical styloid process and broad radial tubercle. 
With the exception of the trapezoid and cuneiform, all the elements of 
the carpus (PI. LIV, fig. 7) are known. The radial surface of the sca- 
phoid is convex transversely and slightly concave in dorso-palmar section. 
Owing to the weathering of its palmar margin, the exact shape of the 
proximal articular surface cannot be determined. Distally, there is a 
broad contact with the magnum, sharply separated from the lunar facet. 
The trapezoidal facet is triangular in outline, deeply concave transversely 
and convex in dorso-palmar section. The facet for the trapezium is 
shaped like a capital B, with the invagination directed toward the inner 
side of the foot. It is almost plane in the dorso-palmar direction. In 
transverse section, the dorsal half of the facet is slightly convex and the 
palmar half concave. The inner posterior angle of the scaphoid supports 
a large hemispherical process, which is wanting in Thylacynus , but present 
