110 MEMOIRS OF THE UNIVERSITY OF CALIFORNIA. 



golds approaching each other quite closely buck to a point about opposite the 

 middle of the orbits. The relation of the pterygoids to the palatines is similar 

 to that in IcIitlii/oNaiirus. The posterior ends of the pterygoids are extended 

 backward as prominent projections reaching a considerable distance behind 

 the basioccipital. Between these processes and the wings of the pterygoids in 

 contact with the qiiadrates there is a strongly marked groove on each side. 



On both sides of the palate of specimen 9950 the posterior portion of what 

 might be considered as the outer wing of the pterygoid is separated from the 

 main body of the pterygoid by a distinct break having the same position in the 

 two cases. If the separation indicated here is a natural parting of the bone, the 

 posterior element evidently corresponds to the ectopterygoid. 



The relations of the prevomers have not been clearly determined, but ap- 

 pear to be similar to those found in Ichthyosaurus. The hyoid elements are 

 long, slender, slightly curved rods similar to the hyoids of Ichthyosaurus and 

 Baptanodon. 



In specimen 9913 an elongated element situated above the pterygoid may 

 represent the epipterygoid. 



The lower jaw is slender and elongated much as in the typical ichthyosaurs. 

 The rami are united in the symphysis for about one-fourth the length of the 

 jaw, and the anterior ends of the splenials are included in the symphysis. The 

 much elongated dentary extends backward to a point almost even with the 

 posterior border of the orbit. The narrowed anterior ends of the angular and 

 surangular extend forward almost as far as the anterior end of the maxillary. 

 In specimen 9950 the outer side of the splenial is exposed for a short distance 

 below the middle of the dentigerous portion of the jaw. 



On the outer side of the posterior portion of the mandible the angular and 

 surangular occupy about the same relative areas as in Ichthyosaurus. No coro- 

 noid elevation is present, but the coronoid region of the surangular is broad- 

 ened and flattened above offering a considerable area for muscle attachment. 

 In specimen 9950 there is on the inner side of the posterior end of the jaw 

 either a coronoid reaching far back, or an element which has been known as 

 the prearticular. In this form the splenial extends back to a point below the 

 coronoid region, where it overlaps the inner plate of the angular. The splenial 

 and the inner plate^of the angular both overlap an element (see Cn., fig. 9, p. 

 27) which extends from the coronoid region almost to the posterior end of 

 the jaw. It extends over the median side of the articular, and is distinctly 

 separated from that bone. The relations of a similar element the writer has 



T> 



seen most clearly in an ichthyosaurian, no. --- , in the British Museum of 



2180 ' , 



Natural History. In this specimen the splenial extends back almost to the 

 cotylus of the mandible, and partly covers the inner, upward-curving portion 

 of the angular. Lying between the splenial and the surangular there is in 



