MIOCENE PORPOISES — KELLOGG 111 



The basicranium and the lateral walls of the braincase are missing; 

 consequently, accurate comparisons cannot be made. The relations 

 and structural peculiarities of the pterygoids and palatines in the 

 region of the narial passages appear to correspond more closely to 

 Inia than with other recent porpoises. 



Each palatine bone is mortised into the ventral surface of the 

 corresponding maxilla and posteriorly overspreads the ventral trough 

 of the vomer, forming the internal surface of the triangular depression 

 in front of the corresponding narial passage. The broken edges of the 

 palatine on each side suggest that a thin external plate of this bone 

 partially, at least, may have overspread this depression. The palatines 

 extend forward almost to the level of the hindmost teeth. 



On the palatal surface, the lateral wall, at least, and also probably 

 the ventral wall, of the ventral portion of each narial passage were 

 formed by the pterygoids. 



The hinder portion of the vomer, which normally widens hori- 

 zontally and sheaths the basisphenoid behind the narial passages, is 

 destroyed. Externally on each side the vomer meets the pterygoid 

 edge to edge and contributes the internal and anterior surfaces of each 

 narial passage. 



On the left side the squamosal is suturally united with the lower 

 border of the parietal and its lateral projection or zygomatic process 

 forms the articular surface for the lower jaw. The glenoid articular 

 surface on the ventral face of the zygomatic process is strongly con- 

 cave, curving upward and forward. The external border of the 

 glenoid facet follows the outer curvature of the zygomatic process, 

 but the external border of at least the posterior half of this surface 

 is set off by a deep groove on the squamosal that undercuts the 

 internal and posterior borders of the facet. The posterior half of 

 the glenoid facet is noticeably widened, and the anterior half is 

 progressively narrowed toward the extremity of the zygomatic 

 process. 



Posterior view: With the exception of the left zygomatic process, 

 the adjoining portion of the squamosal, and the apex of the supra- 

 occipital, all of the posterior wall of the braincase is missing. 



The referred speciman (USNM 20659) consists of a distal section 

 of the rostrum (pi. 11, fig. 1) of a smaller individual measuring 225 mm. 

 in length. Comparison with the skull suggests that the two anterior- 

 most pairs of alveolae are missing on this rostral fragment, since the 

 groove on the lateral surface below the premaxillary disappears at 

 about the level of the third pair of alveolae counting backward from 

 the extremity. On the left side, eight alveolae occupy an interval 

 of 122 mm. 



