JURASSIC PERIOD 87 



variety : but with the exception of sharks, skates, lung- 

 fishes, and forms resembling bow-fins, and herrings, fish-life 

 was not comparable with its present-day representatives. Nor 

 in the Jurassic can many comparisons be drawn. Of fish-life 

 in very deep seas nothing, it may be mentioned, is known. 

 It is not unlikely, indeed, that as yet fishes lived only in 

 shallow and moderately deep waters. 



Sharks flourished in old and new forms. In addition SHARKS 

 to those allied to Port Jackson sharks of our own time, 

 ancestors of " comb-toothed " sharks were now roaming 

 about (Notidanus) ; and sharp-toothed dog-fishes were also 

 in the seas (Scyliida). Angel-sharks, so called from their 

 large wing-like fins, had also appeared (Squatina) : and 

 certain sharks now possessed stout " backbones " rendered 

 flexible by a system of joints (Palaospinax). Skates or rays 

 first known in Carboniferous seas were now well developed 

 (Rhinobatus, Belemnobatis) ; and Chimaeras foreshadowed in 

 Devonian times were represented by various species. 



This was rather a formidable array of fishes that, for the 

 most part, lived and fattened on their gentler brethren. 

 Still, many of the latter were doubtless swifter and more 

 agile swimmers than their foes. They had also, no doubt, an 

 additional if unappreciated preservative in being more 

 prolific. 



The fringe-fumed ganoids (Crossopterygii) still declined. GANOIDS 

 An old family, however, somewhat prominent in the Car- (CROSSOP- 

 boniferous, and consisting of fishes notable for internal TERYGIANS) 

 ossifications, and certain tail-reforms, kept up an imposing 

 appearance (Calacanthida, Undina). 



The key to a highly developed and greatly varied fish- (ACTINOP- 

 life had long been held by the flexibly finned ganoids TBRYGIANS) 

 (Actinopterygii) ; and their ranks, therefore, excite the 

 keenest interest. 



Some members of this Order, it must be admitted, re- 

 mained stationary in development. They still possessed 

 hard, bony scales, and had made little or no progress as 

 regards internal ossification. Their tails, moreover, con- 

 tinued of old type, terminating with the up-curved end of 

 the spinal column (Chondrosteus, Gyrosteus). Some descen- 



