44 



MEMOIRS OF THE UNIVERSITY OF CALIFORNIA. 



In Delphinosannis the caudal series shows a downward curve in the distal 

 region not unlike that in Ichthyosaurus, though the bend is probably not so pro- 

 nounced (fig. 47). The vertebral centra beyond the bend are small, but show 

 some lateral compression, and are slightly higher than the centra immediately 

 in front of the bend. Anterior to the bend in the tail the lower arches appear 

 as long-spined chevrons. The chevrons are not certainly known behind the 

 anterior region of the bend, but may have been present there. The upper arches 



Fig. 51. Clidastes velox Marsh. Caudal series, X Via- (After Williston.) 



Pig. 52. Geosaurus suevicus E. Fraas. Caudal series, X %. (After Fraas.) 



of the centra in the anterior and middle region of the tail are of moderate 

 height and are much flattened laterally. Immediately behind the bend the 

 small upper arches turn sharply forward as in Geosaurus (fig. 52). 



The form of the caudal fin seen in Mixosaurus differs from that in Ichthyo- 

 saurus fundamentally in that the vertical expansion of the fin is produced in 

 a large part by the elongation and erect position of the vertebral arches, 

 whereas in Ichthyosaurus the arches have little or nothing to do with the wid- 

 ening of the fin. Sculling organs of a character somewhat similar to that of 



