5 i6 THE POPULAR SCIENCE MONTHLY. 



known, although in the same formation of Europe Ganoids are abun- 

 dant; and with them are remains of sharks, and some other fishes, the 

 affinities of which are doubtful. The Palaeozoic fishes at present known 

 from this country are quite as numerous as those found in Europe. 



In the Mesozoic age, the fishes of America begin to show a de- 

 cided approach to those of our present waters. From the Triassic 

 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 Catopterus, Ischypterus, Ptycholepis, Mhab- 

 dolepis, and Turseodus. From the Jurassic deposit no remains of 

 fishes are known, 1 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, Elasmobranchs were the prevailing 

 forms, Sharks and Chimaaroids 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, Zamna, and Ptychodus. Among the osseous fishes, Be- 

 ryx, Enchodus, Portheus, and Saurocephalus, were especially common, 

 while the most important genus of Ganoids was Zepidotvs. 



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 Chimseroids, maintained their 

 supremacy, although Teleosts were abundant, and many of them of 

 large size. The Ganoids were comparatively few in number. In the 

 earliest Eocene fresh-water deposits, it is interesting to find that the 

 modern Gar-pike, and Amia, the dogfish 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 suc- 

 ceeding beds, these fishes are still abundant, and with them are Silu- 

 roids nearly related to the modern catfish (Pimelodus). Many small 

 fishes, allied apparently to the modern herring (Chq^ea), left their 

 remains in great numbers in the same deposits, and, with them has 

 been recently found a landlocked ray {Heliobatis). 



The almost total absence of remains of fishes from the Miocene 

 lake-basins of the West is a remarkable fact, and perhaps may best 

 be explained by the theory that these inland waters, like many of the 

 smaller lakes in the same region to-day, were so impregnated with 

 mineral matters as to render the existence of vertebrate life in them 



1 A species of Ccraiodiis has recently been found in the upper Jurassic of Colorado, 

 and named by the writer C. Guniheri. 0. C. M. 



