SINCLAIR! MARSUPIALIA OF THE SANTA CRUZ BEDS. 383 
dyle and the absence of a hook-shaped termination at the proximal end of 
the supinator ridge. In the specimen figured, this is not well shown, 
owing to fracturing of the extremity of the ridge, but it can be satisfac- 
torily determined from the distal end of the humerus of C. lustratus (No. 
15,046). The head is broad and overhangs posteriorly, as in Prothyla- 
cynus. Distally, the trochlear and capitellar surfaces are better defined 
than in the latter genus and the capitellum is separated from the anterior 
margin of the external condyle by a deep groove quite unlike the condi- 
tion in Tliylacynus (text-fig. i, a) and Prothylacynus (PL XLIX, fig. i). 
The anconeal and antecubital fossae are deep, but the connection between 
them shown in the figures (PI. LV, figs. 2, 2 a) is due to accidental rupture 
of the thin lamina of bone separating them. 
The radius (PI. LVIII, figs. 4, 4 a, 5) is intermediate in shape between 
that of Borhyczna and Prothylacynus. The head is oval in outline, as in 
the former genus. The shaft is arched, elliptical in cross section prox- 
imally, but becoming flattened and triangular in cross section toward the 
distal end. The large bicipital tubercle lies on the posterior surface of 
the shaft. 
The ulna is strikingly like that of Prothylacynus , but the sigmoid curva- 
ture of its posterior margin is somewhat more pronounced. The short, 
heavy olecranon is grooved on both sides. The shaft is considerably 
compressed laterally and deeply grooved on the outer side. The ex- 
tremity of the styloid process is hemispherical, but less sharply differen- 
tiated from the radial facet than in Prothylacynus. 
One of the most interesting and important features in the anatomy of 
Cladosictis is the great size and decided opposability of the pollex. The 
feet are preserved with but one specimen (No. 15,046). Unfortunately the 
carpus is incomplete and the articular surfaces of the elements remaining 
have been partly destroyed by weathering. The arrangement shown in 
the figure (PI. LIV, fig. 4) is the same as that of the carpal elements in 
the matrix. The metacarpals are short and stout, interlocking proximally 
and spreading widely distally. The metacarpal of the pollex is a robust 
element with a broad proximal articular surface, convex transversely. 
Distally, the outer condyle is greatly enlarged, deflecting the proximal 
phalanx toward the inner side of the foot. The tip of the ungual phalanx 
of the pollex (PI. LIV, fig. 12) is incomplete, but, so far as preserved, 
shows no indication of a median cleft. Of the remaining metacarpals, the 
