292 Evolution and Distribution of Fishes 



already shown, is undoubted. So in review it may be said 

 that the probable evolution of the Cestracionts was some- 

 what as follows. 



Some primitive type of the Pleuracanthidae seems to 

 have evolved, during early Carboniferous times, at least 

 three divergent types, one of which the Cochliodontidae, 

 became extinct by close of that period. Another, but of 

 which no direct trace exists till the Jurassic period, evolved 

 into the Notidanidae. A third, the Cestraciontidae, prob- 

 ably originated during Carboniferous times but is only 

 known by characteristic teeth named Orodus and Camp- 

 odus. But from the former or a near ally, and during the 

 Permo-Triassic originated Wodnika and later Hyhodus 

 (Fig. 24, p. 193). StWW-Sittr Aero diis a.nd Syne chodus, the 

 palatal teeth of which are at times found fossil in mass, 

 continued the group through the Cretaceous period. De- 

 scendants from some such types again originated the living 

 though now rare species of Port Jackson sharks {Hetero- 

 donttis or Cestraeion) . The above might be represented 

 diagrammatically as in the chart on the preceding page, but 

 for a different set of views and for diagram of a different 

 mode of evolution the reader is referred to Campbell 

 Brown's suggestive paper {2ig). 



The chart that forms Figure 47 (p. 290) will be useful, 

 as illustrating diagrammatically the probable lines of evo- 

 lutionary ascent, and the habitats of fishes already dealt 

 with, or that will be considered later. 



