AVilliston.] Mosasaurs. 139 



is directed rather more directly ventrad. The spine is less stout 

 than in the preceding, and is rather more vertical in position 

 and the anterior thinned part above is more dilated. 



The fifth cervical vertebra differs from the fourth in the 

 broader spine, the stouter transverse processes, and the smaller 

 hypapophysis. 



In the the sixth cervical vertebra the hypapophysis is reduced 

 to a small ossification in some cases, always distinctly smaller 

 than that of the preceding vertebra, and it is directed wholly 

 ventrad. The spine has reached nearly the full width of that 

 of the following vertebrae, though it is somewhat stouter above. 

 The transverse processes are yet stouter. 



In the seventh or last cervical vertebra the hypapophysis is 

 wanting, or is the merest rudiment. The hypapopbysial projec- 

 tion of the centrum is reduced in size, and the centrum in front 

 of it has gradually, assumed the shape of an obtuse carina. 



Dorsal Vertebrae. 



In Clidastes relax there are thirty-five vertebrae between the 

 last cervical and the first non-costiferous vertebra, to which the 

 pelvis Avas, evidently, related. The distinction between the cervi- 

 cals and thoracics cannot be made out from any inherent char- 

 acter, as the last cervical does not bear a distinct hypapophysis. 

 In a series of vertebrae referred to C. pumilus, a species doubt- 

 fully distinct from C. velox, the seventh vertebra bears a short 

 rib. In a specimen of C. velox the eighth post-cranial vertebra 

 has a long rib attached to it, evidently articulating with the 

 sternum. From this it is evident that there are seven true 

 cervicals. Posteriorly, also, there is no distinction between 

 the thoracic vertebrae and those of the lumbar region. All 

 the vertebrae anterior to the pelvic region bear ribs, and 

 all should be considered as dorsal vertebrae, the true tho- 

 racic vertebrae being restricted to those in which the 

 ribs are elongated and inclosing the thoracic cavity, 

 whether connected with a sternum or not. In the anterior 

 dorsal vertebrae the centra are subcarinate below, the ob- 

 tuse, rounded keel becoming less and less apparent until no 



