THE DEVONIAN PERIOD. 489 



been dominant forms in the latter part of the period. The crossop- 

 terygians are now represented by Polypterus of the Nile and Cala- 

 moichthys of South Africa. The Osteolepis (Fig. 223), which was closely 



Fig. 223. — Restoration of Osteolepis by Pander; about one-fourth natural size; from 

 Old Red Sandstone, Scotland. (From Dean and Woodward.) 



in the ancestral line of these modern forms, was abundant in the earlier 

 Devonian. Like the lung-fishes, the crossopterygians appear to have 

 been at or near the climax of their evolution in the Devonian period, 

 though the group continued in considerable strength to the Cre- 

 taceous. 



The actinopterygians are known to have been represented at this 

 time only by the handsome Cheirolepis (Fig. 224), the most primitive 



Fig. 224. — Restoration of Cheirolepis trailli from Old Red Sandstone, N. Scotland. 

 About one-fifth natural size. (After Traquair and Smith- Woodward.) 



of the group, and remarkable among the fishes of the time for the very 

 small size of its scales. It has been found in Scotland and in the 

 Province of Quebec. 



The sharks (elasmobranchs) are now, and (unless the Paleozoic 

 era be excepted) have been throughout known geological time, chiefly 

 denizens of the sea; but they still occasionally live in fresh water, as 

 in Lake Nicaragua and Lake Baikal. It seems clear that in the De- 

 vonian period they lived in the open sea, as heretofore noted, but 

 their remains are also found in the Old Red Sandstone and in the 

 equivalent deposits, and hence it is probable that they lived in fresh 

 and brackish waters also. Prominent among them were the acan- 



