GANOID AND BONY FISH. 21 
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 
(Spatularide), and those Sturgeons (Accipenseridz) 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 paleolithic 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 Devonian 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 Mesolithie epoch out of Ganoid 
fish,and moreover out of the Round-scaled, or Cycliferi. 
