114 



MEMOIRS OF THE UNIVERSITY OF CALIFORNIA. 



concavity is less than in the typical Ichthyosaurus. The excavation is compara- 

 tively slight until about half the distance to the center is reached where it runs 

 in quite sharply. 



The vertical transverse cross-section of the cervical centra is much as in other 

 ichthyosaurians, the transverse diameter being relatively large. In specimen 

 9943 the inferior side of the cervicals is distinctly carinate back to about the 

 tenth vertebra. 



In the dorsal region of specimen 9154, as also in 9950 (pi. 8), and others, 

 the diapophyses are seen to elongate gradually as the centra come to be farther 

 removed from the skull. In the middle dorsal region the lower portion of the 

 diapophysis bends forward rather sharply from the nearly vertical upper 



130 



131 



Figs. 129-131. Cymbospondylus petrinus Leidy. Vertebrae from the middle and posterior dorsal 



regions, X %. 



Fig. 129, middle dorsal vertebra; fig. 130, posterior dorsal vertebra; fig. 131, posterior dorsal 

 vertebra. 



portion. In the typical vertebrae of Cymbospondylus petrinus, the diapo- 

 physes differ from the ordinary form seen in Shastasaurus in that the antero- 

 inf erior border always seems to reach the anterior border of the centrum and 

 be cut off by it (figs. 129 and 130) ; indicating that the lower portion of the rib 

 head has come very near to intervertebral articulation, though there is no facet 

 developed on the posterior border of the centrum in front. 



At about the 36th to 38th centrum in no. 9950 the diapophyses move down 

 the side of the centrum, and the articular faces are no longer confluent with 

 the facets for the neural arches. The form of the centrum also changes from 

 nearly circular in the anterior dorsal region to a high, narrow, triangular form 

 in the posterior dorsal and anterior caudal region (pi. 9, and text-fig. 131). In 



