138 University of Kansas Geological Survey. 



der. The hypapophysis is directed obliquely backward. The 

 atlantar hypapophysis forms the cephalo-ventral part of the 

 centrum, articulating anteriorly with the intercentrum of the 

 atlas, and above suturally with the axis. It bears on its inferior 

 surface a small process directed caudad and ventrad. Between 

 this process and the anterior border of the exogenous projection 

 of the centrum behind there is a deep emargination, the two 

 hyapophyses being separated by a considerable interval. The 

 odontoid process is united to the body of the axis by suture. 

 Its upper surface is nearly horizontal and shallowly concave. 

 The articular surface for lateral pieces and the occipital condyle 

 is oblique and slightly concave from above downward, the upper 

 margin rounded and semicircular from side to side. 



The axis in Platecarpus differs from that of Clidastes in the 

 spine being more prominent in front, in being thicker behind, 

 and in the ball being not at all emarginate above. The hypa- 

 pophysial protuberance is shorter or nearly sessile. The post- 

 zygapophyses stand out more freely, the ridges above them are 

 less prominent. The hypapophysis is entirely free. 



Third to Seventh Cervical Vertebrae. 



Clidastes velox. The third cervical vertebra shows a well- 

 developed zygosphenal articulation posteriorly. The transverse 

 processes are small, only a little larger than those of the axis, but, 

 unlike them, they are strengthened by a ridge running obliquely 

 ventrad and caudad from the under side of the anterior zyga- 

 pophyses. The hypapophysial projection is rather longer and 

 stouter than that of the axis, the hypapophysis itself of about 

 the same size, or a little smaller, and directed, like that, back- 

 ward. The spine is a stout rounded, or trihedral projection, 

 with a sharp carina on the anterior side, less oblique on its mar- 

 gin. The spine is directed rather more obliquely than in the 

 following vertebra?. 



The fourth cervical vertebra has stouter transverse processes, 

 the anterior portion, turned downwards and then forwards to 

 the rim of the cup, is stronger, the oblique ridge leading to the 

 under side of the zygapophyses stouter, and the hypapophysis 



