THE DEVONIAN PERIOD 



591 



Another strange class of organisms related to the fishes, but 

 not true fish, was represented by the singular little lamprey-like 

 cyclostome Palccospondylus (Fig. 422), which, it has been conjec- 

 tured, was really an ancestral lamprey. In any case, this animal 

 represents the vertebrate idea in great simplicity; a slender col- 

 umn of vertebra, modified at one end into a head and finned at 

 the other for a tail, without ribs or paired fins, or any suggestion 

 of limbs, make up the known structure. 



Fig. 423. A partial restoration of Coccosteus decipiens; from the Old Red 

 Sandstone of North Scotland. About ^ natural size. (After Wood- 

 ward.) 



Fig. 424. Dipterus valenciennesi, restoration by Traquair; from the Old 

 Red Sandstone, North Scotland; about % natural size. 



The true fishes found in the supposed fresh-water deposits of 

 the Devonian exceed in number and variety those found in the 

 contemporaneous marine formations. Perhaps the strangest of 

 them were the arthrodirans (Fig. 423), whose relations to other 

 fishes are puzzling, but most paleontologists regard them as a 

 specialized and rather divergent branch related to the ancestors 

 of the lung-fishes (Dipnoi) which reached their climax at about 

 this time. Crossopterygians (fringe-finned ganoids) were present, 



