jKT. 19 A MIOCENE POEPOISE FROM MAEYLAND KELLOGG 19 



Tostratus^ and Delphinus delphis^ attention is at once directed to the 

 similar relationships existing between the bones surrounding the 

 inferior borders of the respiratory passages. Briefly stated, the rela- 

 tions and structural peculiarities of the palatines, pterygoids, and 

 maxillae appear to be more nearly in agreement with Sotalia tucuxi 

 than with any other living porpoise in the family Delphinidae. 

 With the exception of a small fragment of that portion of the thin 

 ascending plate of the palatine which overspreads the pterygoid in 

 front of the supraorbital process, both palatines are destroyed. The 

 sutures which mark the original position of the palatines are well 

 defined and show that they were similar to those of Sotalia tucuxi. 

 In the latter each palatine bone overspreads the elongate depression 

 in front of the corresponding respiratory passage and is suturally 

 united anteriorly and externally with the maxilla. Viewed from the 

 side, the palatine is prolonged upward as a thin ascending plate, 

 which overlaps the pterygoid and abuts superiorly against the hori- 

 zontally expanded cranial plate of the maxilla. This thin ascending 

 plate of the palatine does not appear to have touched the orbito- 

 sphenoid as in Sotalia tucuxi. When the palatines are in their nor- 

 mal positions the elongate depressions are not exposed to view. In 

 the skull of this living porpoise the palatines meet mesially and pro- 

 ject forward beyond the level of the antorbital notches. 



Upon comparing the skulls of Sotalia., Steno, Lissodelphis, and 

 Delphinus with these two fossil skulls it became apparent that each 

 pterygoid in the latter consisted of a single internal plate, which 

 straddles the external margin of the basisphenoid and internally 

 meets the horizontally expanded extremity of the vomer edge to edge. 

 The anterior extremity of the thin internal plate of each pterygoid 

 curves around the outside of the corresponding respiratory passage, 

 forming that much of the lower border, and unites by suture with 

 the palatine below and the vomer above on the anterior wall of that 

 passage. In Sotalia tucuxi the thin internal plate of the pterygoid 

 is continuous anteriorly with a short external reduplication, which 

 in turn united with the above-mentioned thin ascending plate of the 

 palatine. There is a small airspace or sinus between these two 

 plates. No portion of the pterygoid comes in contact with the 

 alisphenoid. 



The vomer first makes its appearance on the ventral surface of 

 the skull about 60 mm. in front of the antorbital notches as a 

 narrow ridge separating the inner margins of the maxillae and is 

 exposed to view for a distance of not more than 40 mm. In front 

 of and posterior to this region the inner margins of the maxillae are 

 in contact and exclude the vomer from the ventral surface of the 

 rostrum. The thin keel of the vomer again makes its appearance 

 near the level of the anterior extremities of the palatines and in- 



