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 Thylacynus, corresponding rather with its position in 

 Sarcophilus, and is much larger than in the former genus, although con- 

 siderably smaller than in Frothy lacynus. 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 Frothy lacynus. 

 The distal end is much deeper than in the latter genus, with the articular 

 surface convex antero-posteriorly, as in Thylacynus, while in Frothylacynus 

 it is concave. The styloid process is longer and heavier than in the last- 

 named genus. 



The ulna (PI. XLV, figs. 2, 2.0} 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 Frothy lacynus. 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 



