During Triassic and Jurassic Periods 201 



are recorded from the Lower Lias, forty-three from the 

 Upper Lias, twenty-three from the Stonesfield Slate, one 

 hundred and forty-two from the Kimmeridge beds, of which 

 one hundred and thirty are included in the Solenhofen 

 list, fifteen occur mainly in the upper lacustrine Portlandian 

 strata, and forty-two in the Purbeck. In contrast, of 

 marine species the Mid Lias is practically destitute of 

 records, as are the Inferior Oolite and Fullers Earth. The 

 Great Oolite and Corn Brash contain species of Hybodus, 

 Acrodus, Aster acanthus and Strophodus. The typically 

 marine Oxfordian and Corallian beds include Notidanus 

 along with the four just named, as also Orthacanthus, 

 Mesodon, Mestunis and Microdon, the last three as de- 

 rivatives from freshwater types (p. 331), Hypsocormiis 

 and Aspidorhynchus (p. 341 ). Each of these is represented 

 by one to three species, rarely as with Notidanus In the 

 Corallian by four species. 



But from the perfect state of preservation shown by 

 species of Squatina (Fig. 26, p. 194), Rhinohatus and 

 Belemnobatis in the lithographic slates of Bavaria, as 

 compared with many of the ganoids, these had probably 

 also become to a greater or less degree marine. Their 

 Increasing abundance also in marine beds of the Cretaceous 

 system likewise favors such a conclusion. 



In stating the above then the writer considers that all 

 of the great groups of fishes continued as inhabitants of 

 the lakes, rivers and swamps, throughout the Jurassic and 

 into the Cretaceous, except for genera of the rays, the dog- 

 fishes, probably some of the pycnodonts like Mesodon and 

 Microdon^ also more doubtfully a few "ganoid" genera 

 like Hypsocormiis and Aspidorhynchus. But even the 

 earlier species of Hybodus and Acrodus that occur in the 

 Lias and Stonesfield Slate, were still largely lake-dwellers, 

 Thus Judd in treating of the Jurassic rocks of N. E. Scot- 

 land (Q. J. Geol. Soc. 29 (1873) 97) gives the thoroughly 

 freshwater list already quoted (p. 192). 



The occurrence here of small specimens of Ostraea and 

 of Mytilus would indicate that occasional Invasions of sea- 

 water may have happened, or even that they had been 

 washed out and redeposited. 



