146 



THE OLDEST FISHES AND THEIR FINS. 



of the fins. How totally different in construction is this 

 kind of fin from that of the perch will be manifest from 



our description and a com- 

 parison of Fig. 49 with Fig. 

 50. Fishes with paired fins 

 like those of the perch may 

 be well termed fan-finned 

 fishes ; while those with fins 

 of the type represented in 

 Figs. 47 and 48 maybe known 

 as the fringe-finned fishes. 



At the present day the only 

 fringe-finned fishes are the 

 Australian lung-fish and the 

 African and American mud- 

 fishes (which, as we have said, 

 are the sole living repre- 

 sentatives of the group of 

 lung- fishes), together with the 

 bichir and an allied species, 

 and the gar-pike, which, as 

 we have seen, belong to 

 the ganoids. All the oldest 

 ganoids, such as those found in the old red sandstone of 

 Scotland (Fig. 48), are, however, likewise of the fringe- 

 finned type ; and since a gradual passage from these 

 primeval ganoids can be traced through later ganoids 

 found in the upper Palaeozoic and Secondary rocks to the 

 bony fishes so characteristic of our present seas and rivers, 

 there can be no manner of doubt but that the fringe- 

 finned type is the most ancient one, and has gradually 

 become modified into the modern fan-finned form. 



The evidence that the fringe-finned type is the oldest 

 does not, however, stop here ; for, curiously enough, not 

 only had the early ganoids and lung- fishes this kind of 

 fin, but the same type likewise obtained in the primeval 

 sharks. The fin-skeleton represented in Fig. 50 belongs 

 indeed to a member of the same group of sharks as does 

 the species of which the entire skeleton is shown in 

 Fig. 51, where the rod-like axis in both pairs of fins is 



FIG. 50. Skeleton of Pectoral 

 Fin of an Extinct Shark. 

 (After Fritsch.) 



