During Triassic and Jurassic Periods 193 



and spines. Hybodus (Figs. 24, 25) and Acrodus however 

 — which may be evolved representatives of the palaeozoic 

 Orodiis and Campodus, extend from the Trias to the Upper 



Fig. 24. Hybodus hauffianus, restored view of fish, from Upper 

 Liassic bituminous shales of Wurtemburg. Fig. 25. Skeleton of 

 H. fraasi from Solenhofen slates. (After Campbell Brown). 



Cretaceous, and were during Triassic times at least, partial- 

 ly if not wholly freshwater. But from the Lower Lias up- 

 ward to the close of the Jurassic, they evidently became 

 largely and at length wholly marine, and continued so till 

 their extinction in the late Cretaceous. The other genera 

 above named, that appeared first in Liassic or in Oolitic 

 strata, either died out during the Jurassic, or persisted in 

 marine surroundings to the close of the Cretaceous, as with 

 Ischyodus. Further a few Jurassic genera, like Squatina 

 (Fig. 26), Rhinohatiis,, and Cestracion, that had taken to 

 marine surroundings, continued alive in one or more species 

 up even to the present day. 



So while it is possible to speak only with a fair degree 

 of accuracy, the evidence seems sufficient to warrant the 



