WILLISTON AND CASE: KANSAS MOSASAURS. 23 



chevrons are strongly oblique throughout the series and are firmly 

 co-ossified with the centrum. 



The tail, it is thus seen, has a broad, vertical, fin-like extremity, 

 which, doubtless, aided much in the propulsion of the animal through 

 the water. 



There are sixty-seven vertebrae with chevrons present in the speci- 

 men, all continuous, except in one place. The last one is less than 

 one-fourth of an inch in diameter, and shows that there had been yet 

 another, possibly several more. Toward the base of the series the 

 tail has been bent forwards over the back, and it is possible that, 

 where the break occurs, there has been a vertebra lost. The measur- 

 ments, however, do not seem to indicate any loss. The entire series 

 of vertebrae was not less than sixty-eight, and probably not more than 

 seventy, making for the entire vertebral series one hundred and 

 seventeen to twenty. 



MEASUREMENTS OF THE CHEVRON-BEARING CAUDAL VERTEBRAE. 



I. Length to rim of ball 26 millim. 



5. Length to rim of ball 24 



Vertical diameter of ball 21 



Transverse diameter of ball 24 



10. Length to rim of ball 24 



15. Length to rim of ball 24 



Height of spine above floor of neural canal 40 



Length of chevron 45 



20. Length to rim of ball 23 



Vertical diameter of ball 21 



Transverse diameter of ball 22 



25. Length to rim of ball 20 



Height of spine 44 



Width of spine at base 19 



Width of spine at distal end 10 



Length of chevron 85 



Altitude of tail 112 



30. Length to rim of ball 18 



Vertical diameter of ball 17 



Height of spine 57 



Width of spine at base 19 



Width of spine at distal end 9 



Length of chevron 99 



Altitude of tail 120 



35. Length to rim of ball 16 



Vertical diameter of ball 16 



