GANOID AND BONY FISH. 2 I I 



Ludlow strata). Gigantic species of them, coated with 

 strong bony plates, are found in the Devonian system. 

 But of this legion there now lives only the small order 

 of Sturgeons (Sturiones), including the Spade-sturgeons 

 (Spatularidse), and those Sturgeons (Accipenseridse) to 

 which belong, among others, the Huso, which yields isinglass, 

 or sturgeon's sound, and the Caviar-sturgeon, whose eggs 

 we eat in the shape of caviar, etc. Out of the mailed 

 Ganoid fish, the angular and round-scaled ones probably 

 developed as two diverging branches. The Angular-scaled 

 Ganoid fish (Rhombiferi) — which can be distinguished at 

 first sight from all other fish by their square or rhombic 

 scales — are at present represented only by a few survivors, 

 namely, the Finny Pike (Polypterus) in African rivers 

 (especially the Nile), and by the Bony Pike (Lepidosteus) 

 in American rivers. Yet during the palseolithic and the 

 first half of the mesolithic epochs this legion formed the 

 most numerous group of fishes. The third legion, that of 

 Round-scaled Ganoid fish (Cycliferi), was no less rich in 

 forms, and lived principally during the Deyonian and Coal 

 periods. This legion, of which the Bald Pike (Amia), 

 in North American rivers, is the only survivor, was 

 especially important, inasmuch as the third sub-class of 

 fish, namely. Osseous fish, developed out of it. 



Osseous fish (Teleostei) include the greater portion of the 

 fish of the present day. Among these are by far the 

 greater portion of marine fish, and all of our fresh-water 

 fish except the Ganoid fish just mentioned. This class 

 is distinctly proved by numerous fossils to have arisen 

 about the middle of the Mesolithic epoch out of Ganoid 

 fish, and moreover out of the Round-scaled, or Cycliferi. 



