SELACHOIDEI. 



329 



opposite to the space hetween pectoral and ventral fins ; anal fin 

 present. Nasal and huccal cavities confluent. Teeth ohtuse, 

 several scries being in function. 



This family is one of particular interest, because re- 

 presentatives of it occur in 

 numerous modifications in 

 primary and secondary strata. 

 Their dentition is uniformly 

 adapted for the prehension 

 and mastication of crusta- 

 ceous and hard-shelled ani- 

 mals. The fossil forms far 

 exceeded in size the species 



of the only surviving genus; Fig- 119. -Jaws of Port Jackson Shark, 



Cestracion pliilipisi. 



they make their appearance 



with Ctenoptychius in the Devonian ; this is succeeded in 



Fig. 120. — Upper jaw of the same, half natural size. 



the coal-measures by Psammodus, Ghomatodus, Petrodus, Coch- 



