THE DEYOXIAX PERIOD. 



487 



supposed fresh-water deposits of the Devonian exceed in number 

 and variety those found in the contemporaneous marine formations. 

 Their relative abundance, however, changed notably during the succeed- 

 ing periods until the sea fishes came to preponderate over the fresh- 

 water fishes. Some of the leading types seem to have flourished in 

 the fresh waters, while it is doubtful whether or not they had any real 

 representation in the sea, though their remains are occasionally found 

 in marine deposits. Tins is of interest in connection with the question 

 of the original habitat of the vertebrates, a question to which the 

 new views of the ostracoderms give fresh point. 



Perhaps the strangest of the fishes were the arthrodirans repre- 

 sented by Coccosteus and its allies, Fig. 219. The Coccosteus was well 



Fig. 219. — A partial restoration of Coccosteus decipien-?; from the Old Red Sandstone 

 of North Scotland. (After Woodward.) About one-fourth natural size. 



protected by plates upon its head and shoulders but not on its pos- 

 terior parts, of which little is known. The relations of the arthro- 

 dirans to other forms are puzzling, but most paleontologists regard 

 them as a specialized and rather divergent branch related to the ances- 

 tors of the lung-fishes. 



The lung-fishes (Dipnoi) formed a notable feature in the fauna. 

 This was perhaps even the time of their maximum development and 

 specialization. It is a matter of interest that they were more abundant 

 in the fresh-water faimas than in the marine, as it is in line with the 

 fact that they are now wholly confined to fresh waters, being repre- 

 sented by a few strangely isolated forms, viz., Ceratodus in Australia, 

 Protopterus in Africa, and Lepidosiren in South America. The Dipterus 

 (Fig. 220), a representative form found in the Old Red Sandstone of 

 north Scotland, had the outlines of a typical modern fish and was 

 completely covered with scales. 



The crossopterygians (fringe-finned ganoids), at present the most 

 favored claimants to the parentage of the amphibians, were repre- 



