EXTINCT ANIMALS 



were very abundant in ]\Iesozoic and Palae- 

 ozoic times, and have left their hard scales in a 

 very perfect state in the ancient rocks of those 

 periods. They had often unequally divided 

 triangular tail-fins, and in internal structure 

 were hke the sharks rather than the modern 

 bony fishes. Very few of these Ganoid fish 

 survive to the present day, but a fine one, the 

 Polypterus (Fig. 178), still lives in the Nile and 

 other African rivers, and anotiier, the bony 

 pike or Lepidosteus, in the North American 

 lakes. The sturgeon also belongs to this set 

 of fishes. In the Devonian is found, together 

 with many others, a beautifully preserved fish, 

 the Osteolepis (Fig. 180), which had lobed fins 

 and hard bony scales like the Polypterus of the 

 Nile. Allied to these Ganoid fishes, but differing 

 in the fact that they possess lungs as well as 

 gills and have very peculiar lobate fins, are the 

 so-called mudfish of Africa (Protopterus) and of 

 South America (Lepidosiren). A third mud- 

 fish is found in the rivers of Queensland, Aus- 

 tralia, and is now living in the Zoological Gar- 

 dens in London. It is called Ceratodus (Fig. 

 181), and is obviously related to some very 

 ancient extinct fishes, of whose race it is a last 



248 



