276 



PALAEOZOIC TIME — DEVONIAN AGE. 



There are also among the remains in the Corniferous beds species of Cepha* 

 laspis resembling the European (fig. 517), and of Holoptychius (near fig. 518); 

 but no figures of them have yet been published. 



Fig. 460. 



Fig. 461. 



Fig. 460, Head of Macropetalichthys Sullivanti Newberry (X %)\ 461, Tooth of same. 



These earliest of American fishes belong to two out of the three 

 grand divisions of the class : — 



First, the Selachians, or sharks. 



Secondly, the Ganoids, or fishes having the body covered with 

 shining bony scales or plates. This order of Ganoids, once exceed- 

 ingly numerous in species, is now nearly extinct: it is represented 

 by the Gar-pike and Sturgeon of existing waters. 



The third grand division — that of the common osseous fishes, or 

 Teliosts, which includes the Perch, Salmon, etc. — was not introduced 

 until near the close of the Reptilian age, in the Cretaceous period. 



The Selachians of the Devonian age belong to the Cestraciont 

 family of sharks, — a group in which the mouth is furnished with a 

 pavement of large bony plates instead of teeth, and which have 

 the first ray of the dorsal fin a large and stout spine (figs. 464, 470). 



The Devonian Ganoids are of three kinds: — (1) Placoganoids, 

 having the body covered with plates instead of scales (like fig. 516) ; 

 (2) Rhombifers, having rhombic scales, and these arranged like tiles 

 (as in figs. 473, 475, 519) ; and (3) Imbricates, having the scales ar- 

 ranged like shingles, as in Holoptychius (fig. 518) and other Ccela- 

 canths, and the modern Amia. 



All these ancient fishes have vertebrated tails, — that is, the verte- 

 bral column extends to the extremity of the tail (figs. 519, 603), 

 instead of stopping short at its commencement (fig. 473) as in 

 nearly all existing fishes. In most of these vertebrate-tailed 

 species the vertebral column extends into the upper lobe of the 

 tail, and the two lobes are very unequal, as in figs. 464, 519, 617 : 



