20 



.MK.MOIRS OF THE UNIVERSITY OP CALIFORNIA. 



are situated much as in the later ichthyosaurs. The quadratojugal forming the 

 outer boundary of the quadrate foramen is overlapped superiorly by the supra - 

 temporal. The inferior border of the quadratojugal extends forward and above 

 the inferior temporal notch to meet the jugal. 



Palatine Region. The palate of Cyntbospoiidylus (fig. 7) closely resembles 

 that of Ichthyosaurus in most details of its structure. The roof of the mouth is 

 largely covered by the expanded palatines and pterygoids, the median margins 

 of the pterygoids approaching each other closely for a considerable distance 

 back toward the basisphenoid. The pterygoids are characterized by promi- 

 nent posterior projections of the median edges, which extend some distance back 

 of the basioccipital. In specimen 9950 the posterior portion of the lateral wing 

 on each of the pterygoids is separated from the main body of the bone in such 

 a manner as to suggest that it represents a distinct element (fig. 7, x). If 

 there is a separate bone here it is evidently a discrete ectopterygoid which has 

 united with the pterygoid in all later forms. 



Sp 



Fig. 8. Merriami zitteli (Merriam). Skull, lateral view, X %. An, angular; Sa, surangular; Sp, 

 splenial; D, dentary; MX, maxillary; L, lachrymal; J, jugal; Pto, postorbital; S, sclerotic ring. 



Mandible. The lower jaw of Gymbospondylus is formed much as in the 

 later ichthyosaurian genera, the relations of the several elements as they ap- 

 pear on the outer side of the rami being much as in Ichthyosaurus. In the 

 genus Merriamia (fig. 8) possibly also in Mixosaiirus, the surangular is rela- 

 tively large and forms the principal part of the outer side of the posterior 

 half of the jaw. In Cymbospondylus it forms the anterior side of the cotylus 

 for the quadrate, and is thickened transversely anterior to the cup. As in the 

 other ichthyosaurian genera there is no coronoid elevation, but the surangular 

 presents a broad flat superior surface in the region of the coronoid. Below the 

 coronoid margin there is, as in Baptanodon, a relatively small lamellar bone 

 extending back almost to the posterior extremity of the inner side of the jaw 

 (fig. 9), and representing the coronoid or the prearticular. The articular ex- 



