284 



Lines, 



Depth of jaw below fourth tooth 11 



I >epth of jaw at the outer side of the glenoid articulation 24 



Length of projection back of the glenoid articulation 20 



Transverse diameter of glenoid articulation 18 



Vertical diameter of glenoid articulation 16 



An axis and a dorsal vertebra accompanying the former specimens probably 

 pertained to the same individual. They are both considerably distorted from 

 pressure at the sides. 



The axis is rather longer than that of C. intermedins, while its hypopophysis 

 is considerably smaller at the extremity, and the ball of the centrum is more 

 uniform in diameter, or is less emarginate above. The lower element of the 

 atlas remains in firm sutural connection with the body of the axis, but the 

 odontoid element of the latter and the lateral elements of the atlas are absent. 



The dorsal specimen retains the neural arch with its characteristic zygan- 

 tral articulation. 



Measurements of the vertebrae are as follows : 



Lines. 



Length of axis through center of the body 22 



Width of ball of body of axis 10J 



Height of ball of body of axis ; . . 10J 



Length of body of dorsal vertebra inferiorly 22 



Accompanying the former specimens there are several others which, if 

 they did not pertain to the same individual, probably belonged to the same 

 species. . 



Two fragments of the upper part of the cranium represented in Fig. 8 

 resemble the corresponding portions in Clidastes propython, as described and 

 figured by Professor Cope, and differ only in the greater size. Fig. 9 repre- 

 sents an isolated basi-sphenoid bone, probably from the same skull. 



These skull-fragments indicate an animal about one-third larger than C. 

 propython, as described by Professor Cope. 



It is a question of some importance how far difference in size among the 

 mosasauroids may be a test of difference in species. Among the numerous 

 remains of these animals which have been discovered I have never yet 

 observed any which presented any evidence relating to age. In no case 

 have I seen a vertebra in which the neural arch was not continuous with the 

 centrum, so that I have been led to suspect that the former grew out of the 

 latter, as in most fishes, and was never united with it by articulation, as in 

 the crocodiles, &c. In this view of the case, some of the many described 



