The Chondrostei and Holostei 



333 



Fig. 55. Mesodon macropterus, a freshwater pycnodont fish 

 from the Solenhofen or Lithographic Stone of Bavaria, restored 

 by A. S. Woodward. The surface and skeletal aspects are shown, 

 and the larger head bones are lettered. Somewhat reduced in size. 

 (After A. S. Woodward). 



of the species that compose these have been recorded from 

 the freshwater beds of Ain and Cerin in France, from the 

 lithographic stone of Altmiihl in Bavaria, or from the still 

 higher Portlandian and Purbeckian beds. 



In passing now, however, to Gyrodus and Coelodus, a 

 new habitat-relation seems gradually to have been estab- 

 lished. For while one or other of these occurs from the 

 Kimmeridge Clay through Purbeck to freshwater Wealden 

 beds, about the time of deposit of the Neocomian or Gault 

 on through Cenomanian to Senonian deposits, the remains 

 of both are found in Chalk strata, and alongside selachians 

 which by this time had reinvaded and repopulated many 

 seas. 



