55 



while the Teleodei, or time l)ony fishes, which so largely predominate 

 at the present day, did not appear on the scene of life until the 

 formation of the Cretaceous rocks. * Seven, or eight, living genera 

 alone survive of the Ganoklel which prevailed so numerously in 

 Palaeozoic times, and but one of these, the sturgeon, the least 

 characteristic of the group, is found in European waters. Two 

 of the six remaining forms, wliich are all dwellers in freshwater, 

 occur in Africa, and four inhabit the lakes and rivers of Xorth 

 America. The i)reservation of the majority of living ganoids in 

 America is probabl}^ o'n'ing to the fact that some portions of this 

 ancient continent, truly the old world of geologisU, have never 

 been submerged since their upheaval from the first Silurian seas, 

 thus some rejiresentatives of this ancient race of fishes were able 

 to find a refuge in its bays and rivers, and the chain of descent 

 has been kept un])roken from the early ages of the incalculably 

 remote past. 



The large spined, shagreen scaled Acanthodido?, which are 

 considered by Professor Huxley to link the ganoids to the 

 Elasmobranchs, range from the Devonian to the Permian rocks. 

 The "thick toothed" Pycnodonts lived from the coal measures to 

 the Tertiaries, and are now extinct, while the buckler-headed 

 Ccpluilespids, like the Placnderms, existed onl}- in Silurian and 

 Devonian times. The CJioiidrosteida', to which group the sturgeons 

 1)elong, were certainly represented in the Jurassic seas, and 

 possibly by the gigantic Macropctalkhthis in the Devonian. Amia 

 cnlva, the dog-fish of the American lakes, is the sole member of 

 tlie sub-order Amiadce. The LepiSosteidce includes the hving bony 

 pikes, inhabitants of the rivers of the same continent, and fossil 

 forms in all the formations reaching back to the Devonian. 



There remains for discussion but the sub-order Crossoj)- 

 I'-ryghlrr., that important group of fringe-finned ganoids, through 



* A species of Polyodon allied to the Sturgeon, inhabits the rivers of 

 Xortheru China. 



