452 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 52 



outline almost at right angles with it. The outer lip is very high pos- 

 teriorly. The inner lip is also high, and is peculiar in that it is 

 divided longitudinally below the middle by a distinct groove, resem- 

 bling the median inferior groove. Viewed from above, the great 

 breadth of the bulla, its rectangular outline, and the breadth of the 

 Eustachian canal are especially noticeable. The upper border of the 

 inner lip is only slightly emarginate. A principal feature of the 

 under surface of the bulla is the great breadth of the groove between 

 the two lips, or lobes. It is quite deep as well as broad, and extends 

 to the anterior end of the bulla (as far as preserved), dividing it into 

 two nearly equal portions. The two lobes are nearly equal in size 

 and downward extension, differing greatly in the latter respect from 

 such forms as Mesoplodon, Berardins, etc. The posterior end of the 

 outer lobe, or lip, is well rounded, but that of the inner lobe is 

 strongly compressed, presenting a prominent thin ridge, directed 

 obliquely upward and outward. The interior of the bulla, as in 

 Scluzoddphis, presents two pits separated by a rounded, transverse 

 ridge. The posterior pit, or concavity, is much the deeper. 



The dimensions of the bulla are as follows : Greatest length (as 

 preserved), 50 mm. ; greatest breadth, 36; greatest height, 30; trans- 

 verse breadth of the involuted portion of the inner lip, 20. 



Periotic Bone 



The right periotic bone (fig. 78), which is the one preserved, is 



small and of a peculiar form, unlike that of any living toothed whale 



with which I am acquainted, but 



:^ somewhat resembling that of 



" ^ Bcrardhis and other ziphioid 



genera. The bone is a little 



abraded, but not so much as to 



materially alter its original form. 



Viewed from within, the anterior 

 Fig. 78. — Periotic bone of Prosqua- , u j • . 1 r 



, J ^ ,• T J 1 1 petrous body is separated from 



lodon aiistrahs Lvdekk. '■ ■' ^ 



Inferior surface. Nat. size. ^he remainder of the bone by a 



deep emargination below, and is 

 oval in outline, and moderately bent downward. The convex portion 

 of the periotic containing the cochlea is small, and the internal porus 

 aciisticus oval and oblique. The superior outline of the main mass 

 of the bone when viewed from the inner side is nearly straight, but 

 that of the anterior petrous body is inclined downward at an angle of 

 45°. The process for the articulation of the tympanic, which is seen 

 on the under side of the bone, is small, and its inner margin ovei"- 

 hangs the short, curved canal for the facial nerve. 



