THE TEETH OE FISHES 91 



teeth vary greatly as to size, and in former geo- 

 logical ages sharks existed whose teeth, found in 



Fig. 30-A. — Roentgenogram of tooth of extinct Shark. (By E. H. 

 Skinner.) 



the tertiary rocks, are of such large size that their 

 possessors must have been enormous (Fig. 30-A). 

 These teeth measure five by six inches. The gen- 



