SELACHOIDEI, 



329 



opposite to the space hetiveen p>ectoral mid ventral fins ; anal fin 

 present. Nasal and huccal cavities confiuent. Teeth ohtuse, 

 several series being in funetion. 



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 i / 

 and mastication of crusta- \ 

 ceous and hard-shelled ani- 

 mals. The fossil forms far 

 exceeded in size the species 



of the only surviving jrenUS ; ^ig- I19.-Jaws of Port Jacksou Shark, 

 ■^ . Cestracion philippi. 



they makQ 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, Chomatodus, Petrodus, Coch- 



