In the Mesozoic age, the Fishes of America begin to show a 

 decided approach to those of our present waters. From the 

 '^Friassic rocks, Ganoids only are known, and they are all more 

 or less closely related to the modern Gar-pike, or Lepidosteus. 

 They are of small size, and the number of individuals 

 preserved is very large. The characteristic genera are, Catop- 

 iei'us, Ischyptenis, Ptycholepis, Rhahdolepis, and Turneodns. 

 From the Jurassic deposits, no remains of fishes are known, 

 but in the Cretaceous, ichthyic life assumed many and 

 various forms ; and the first representatives of the Teleosts, 

 or bony fishes, the characteristic fishes of to-day, make 

 their appearance. In the deep open sea of this age, Elas- 

 mobranchs were the prevailing forms. Sharks and Chimgeroids 

 being most numerous. In the great inland Cretaceous sea of 

 North America, true osseous fishes were most abundant, and 

 among them were some of carnivorous habits, and immense 

 size. The more sheltered bays and rivers were shared by the 

 Ganoids and Teleosts, as their remains testify. The more 

 common genera of Cretaceous Elasmobranchs were, Otodus, 

 Oxyrhina^ Galeocerdo^ Lamna and Ptychodus. Among the 

 osseous fishes, Beryx^ Enchodiis^ Portheus and Saurocephalus 

 were especially common, while the most important genus of 

 Ganoids was Lepidolus. 



The Tertiary fishes are nearly all of modern types, and from 

 the beginning of this period there was comparatively little 

 change. In the marine beds. Sharks, Rays and Chima^roids 

 maintained their supremacy, although Teleosts were abundant, 

 and many of them of large size. The Ganoids were compara- 

 tively few in number. In the earliest Eocene fresh-water 

 deposits, it is interesting to find that the modern Gar-pike, 

 and Amia, the Dog fish of our western lakes, which by their 

 structure are seen to be remnants of a very early type, are 

 well represented by species so closely allied to them that only 

 an anatomist could separate the ancient from the modern. In 

 the succeeding beds, these fishes are still abundant, and with 

 them are Siluroids nearlv related to the modern Cat-fish 



