PALEOZOIC ROCKS AND ERA. 



The first is an Australian fresh-water fish, the recently 

 discovered Ceratodus (horn-tooth) (Fig. 215). The sec- 

 ond, Lepidosiren (scale-siren), is a very curious animal, 

 intermediate between fish and reptile, found in South 

 America and Africa (Fig. 216). The third is the gar- 

 fish, Polypterus (many fins), from the Nile (Fig. 217). 

 The fourth is the only living representative of cestraciont 

 sharks the Cestracion of Australian seas (Fig. 218). 



Bearing- on Evolution. It is a curious fact that 

 these fishes, which are most nearly allied to Devonian 



FIG. 215. 



FIG. 216. 



FIGS. 215, 216. Nearest living allies of Devonian fishes : 215. Ceratodus 

 Fosterii, x T V (After Gunther.) 216. Lepidosiren. 



fishes, are by no means low in the scale, but, on the 

 contrary, are, in some respects at least, very high. 

 But one thing is very noteworthy, viz., that they all 

 have amphibian characters united with fish characters 

 they are all connecting links between fish and amphi- 

 bian. For example, it is seen that the vertebral col- 

 umn in these, and still more in their Devonian allies, 

 runs far into, often to the end of, the tail-fin. The 

 tail-fin is vertebrated. The tail vertebrae are finned on 

 the sides. This is universal in Devonian fishes. Again, 



