AVilliston.] Mosasaurs. 183 



neural canal. This shorter axes are oblique, i. e. , make less than 

 a right angle with the long axis of the centrum ; and the articular 

 surface of the ball is thus carried forward on the upper face to 

 much nearer the base of the neurapophysis than usual, in the 

 anterior vertebra nearly touching them. The ball is, likewise, 

 more convex than in any other species, having a slight central 

 prominence in the posterior vertebra. There is no annular 

 groove around the ball. In both, the articular surface of the 

 hypapophysis is truncate and bounded by an elevation in front, 

 a peculiarity not observed in any of the species above described. 

 There is no trace of a zygosphene in either. In the anterior 

 vertebra the diapophyses are nearly horizontal ; the posterior 

 portion slightly thickened and oblique. The anterior portion 

 is thinned out, and very rugose above and below, and does not 

 continue its margin into the rim of the cup. In the second 

 vertebra the diapophyses are very large, vertical, and with a 

 horizontal portion rising in a curve to join the middle of the 

 lateral margin of the cup. Neural spine narrowed above and 

 keeled behind. 



"Length of centrum of anterior vertebra 64mm. 



Vertical diameter of ball 30 



Transverse diameter of same 39 



Length of posterior vertebra 64 



Vertical diameter of ball 30 



Transverse diameter of same 43 



Expanse of the anterior zygapophyses 55 



Platecarpus tectulus. 



Holcodu8 tectulus Cope, Proc. Amer. Phil. Soc, Dec. 1871. 



Platecarpus tectulus Cope, Cret. Vert., 159, 269, pi. xxi, ff . 3-6; xxvn, ff. 5-10. 



" Established on a number of cervical and dorsal vertebrae of 

 smaller size than those characteristic of the other species of the 

 genus. The centra have not suffered from distortion under 

 pressure. The articular surfaces are depressed transverse- 

 elliptic in outline with a slight superior excavation for the 

 neural canal. A well-marked constriction surrounds the ball. 



"There is a rudimental zygosphene, in the form of an acute 

 ridge rising from the inner base of the zygapophysis, and unit- 



