60 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62. 
rowing of the head. A well-defined facet represents the tubercle. 
There is a marked lengthening of theshaft. A shortening of the neck 
which accompanies the uplifting of the head tends to impart a more 
even curvature to the shaft of the fifth rib (pl. 16, fig. 4) on the left 
side. The angle formed by the neck with the shaft is most noticeable 
in the first rib as remarked above and becomes less acute in each 
succeeding rib. The shaft in the region of the tubercle is consider- 
ably narrower than the third and slightly less than the fourth rib. 
This narrowing of the rib in the region of the tubercle and shortening 
of the neck is carried even further in the sixth rib (pl. 16, fig. 5) 
belonging to the left side. The eleventh rib (pl. 16, fig. 6) resembles 
in some respects the same rib of Inia geoffrensis. The shaft is a little 
wider than some of the preceding ribs. The head is squarely trun- 
cated; the shaft is expanded near the center of the proximal half and 
the distal end is so twisted that it is at right angles to the proximal 
end of the shaft. 
ULNA. 
In general outline, the ulna (pl. 6, fig. 2) differs somewhat from that 
of Basilosaurus cetoides.8 The shaft is proportionately shorter; the 
olecranon process and the proximal end of the ulna beyond the open 
greater sigmoid cavity are relatively smaller. This cavity on the 
anterior face of the ulna possesses an indistinct margin superiorly and 
the slope of the articular surface would permit considerable freedom 
of movement of the paddle. The olecranon process is not perfectly 
preserved, and what remains of the original surface is sufficient to 
justify the assumption that the original form was essentially similar. 
On the anterior face of the ulna and immediately below the sigmoid 
cavity is a depressed articular surface for the corresponding portion 
of the radius. The shaft of the ulna is relatively stout, quite broad, 
and thin. The anterior face of the shaft is rounded; the external and 
internal faces converge posteriorly to form a thin margin. The sur- 
face of the bone is smooth and the distal end is squarely truncated. 
MEASUREMENTS FOR THE SKULL. 
mm, 
Total idength i éi'skullias presefved . 10 1812: SAU0IG. Ae BO 750 
Length of rostrum as preserved (maxillary notch to tip of beak).........-.-- 485 
Greatest breadth of skull across supraorbital processes.....----..------------ 270 
Greatest breadth of skull across zygomatic processes of squamosal............ 290 
Vertical height of skull (between tip of descending free plate of basioccipital 
and ‘frontals'on'thetvertex’or thetskull))-) et. <2 Se eae sn enle Me wiwiecnin oe oe 174 
Vertical height of skull (basisphenoid to frontals on vertex of skull).........- 123 
Greatest height of skull at base of rostrum (across maxillary notches)......... 76.5 
Total length of, maxillae.as presenyed -« - m5. <i oe ope <a emcee < sre - tier «fe eps 578 
Greatest breadth across premaxillae at line of anterior margin of mesethmoid. 90 
Greatest breadth across premaxillae at line of anterior margin of nasals....... 68 
83 Gidley, J. W., Proc. U.S. Nat. Mus., vol. 44, No. 1975. fig. 1, p. 651, 1913. 
