NO. 1875 ^^^ F'OSSIL, CIvTACEAN — TRUE 443 



On the under surface of the frontal plates the most conspicuous 

 feature is the optic canal, which is deep proximally, and runs at an 

 angle of 45° with the longitudinal axis of the skull. It dies away 

 distally, before reaching the free margin of the orbit. 



The larger fragment of the skull consists of the occipital, squa- 

 mosal, and parietal bones. The basioccipital^ is somewhat fractured, 

 and the inferior surface has been abraded and more or less altered 

 by chiseling. It is broad and nearly flat medially, and appears not 

 to have had the transverse ridge which is so noticeable in Inia. The 

 lateral free margins are thick. 



Nearly all of the median portion of the supraoccipital is lacking, 

 but the general surface appears to have been nearly plane, with the 

 lateral margins nearly parallel and the anterior margin forming an 

 obtuse angle. The occipital crest is low and broad, with sloping 

 sides, rather than thin and erect, as in Inia. It appears not to have 

 been greatly thickened anteriorly, as it is in Inia. Posteriorly it dies 

 away altogether, so that there is no barrier between the squamosal 

 and occipital. This conformation is due to the small extension of 

 the temporal fossae posteriorly, as compared with Inia and many 

 of the Delphinidse. The exoccipitals are oblong, broad, nearly flat, 

 and but little inclined backward. They resemble the same parts in 

 Balccnoptera and other whalebone whales, rather than in Inia. The 

 occipital condyles are rather narrow, and do not project much from 

 the surface of the occipital bone. 



The squamous portion of the temporal is oblong and slightly con- 

 cave below, and is separated from the zygomatic process by a very 

 shallow groove. The latter process is short and convex externally, 

 and appears to have been moderately acute anteriorly, but the apex is 

 broken off on the left side, while on the right the whole process is 

 lacking. The free margin of the zygomatic process is thin, and the 

 postgenoid is well developed, thin, and directed downward. The 

 interval between it and the exoccipital is small relatively. The tem- 

 poral fossa gets its great breadth chiefly from the breadth and in- 

 clined position of the parietal bone, and very little from the lateral 

 extension of the zygomatic process, the root of which is very short. 



The glenoid surface is broad and only moderately concave, and is 

 rendered uneven by several low, rounded, transverse ridges. The 

 inferior mastoid surface is broad and concave. The periotic region, 

 unlike that of Inia, is quite smooth, but the position of the various 

 vacuities and foramina cannot be determined. 



* I am not sure that a portion of the basisphenoid is not attached to this. 



