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JOURNAL OF MAMMALOGY 
than in Eumetopias jubata. The inferior face of the shaft (fig. Ic) is somewhat 
flattened, being slightly twisted on the long axis from the external to the in- 
ternal side. The surface of the shaft is missing in the area where the olecranon 
fossa should occur, extending inward as far as the inferior margin of the inner 
condyle. 
Left Humeeus of Pliopedia pacifica X No. C. 537, Stanford University 
Santa Margarita, California: fig. Id, distal view 
The trochlear surface (fig. Id) for articulation with the bones of the forearm 
is divided into an outer and less convex capitellum articulating with the radius, 
and a trochlea articulating almost entirely with the ulna, though to some 
extent with the inside of the proximal facet of the radius. From an inferior 
view (fig. Ic.), the trochlea is observed to be convex from above downward 
and concave from side to side. It is limited internally, externally, and proxi- 
mally by a sharp crest. 
The inner condyle is a triangular tuberosity projecting internally and slightly 
backward; its anterior surface is a continuation of the internal surface of the 
shaft and is bounded medially by the coronoid fossa. The outer condyle is 
much less prominent than the inner. The external surface is a continuation down- 
ward of the supinator ridge. It is convex from above downward, forming a shal- 
low crescentic concavity between its inferior margin and the rounded edge of 
the capitellum. 
In its general form the ulna (fig. 4.a) was undoubtedly much like that of Eu~ 
metopias jubata (fig. 5), or that of Odobenus divergens, but with the distal end 
much stouter and broader. It is very much larger than the radius, as in other 
pinnipeds. The olecranon process and the proximal end of the ulna beyond' 
the semicircular greater sigmoid cavity are missing. This articular surface on 
the anterior face of the ulna for the trochlea of the humerus is characterised by 
an evenly concave curve, wider above than below; its proximo-distal diameter (fig. 
4b) is proportionately greater than in Eumetopias jubata. Immediateh" below 
the greater sigmoid cavity and on the external face there is a shallowly concave 
articular surface vrhich receives the head of the radius. Below this lesser sig- 
moid cavity is a small rounded tuberosity which articulates with the tubercle 
on the postero-internal margin of the shaft of the radius (fig. 6c). No trace of 
this tuberosity is observed on the ulna of Odobenus divergens or of Zalophus 
