Anhnah Before Man 



them has endured to modern times, the most 

 common representative being the Port Jackson 

 shark, Cestracion jpliilippi^ a small and inoffen- 

 sive species found in Australian waters. 



In other ancient sharks teeth w^ere repre- 

 sented by a single, more or less spirally twisted 

 and ridged plate, and as this suggests a snail- 



>^-. 



Lower tooth-plate of a cochliodont shark. Somewhat reduced. 

 (After Worthen.) 



shell, these have been termed cochliodont. 

 Teeth like these were evidently fitted only for 

 crushing, and for crushing comparatively fragile 

 things at that, so that these cochliodonts prob- 

 ably lived on crabs or thin-shelled mollusks, 

 possibly on the abundant brachiopods. The 

 structure of this tooth -pi ate is very much like 



106 



