582 Arthrodires 



between the two is usually a huge joint which Dr. Dean com- 

 pares to the hinge of a spring-beetle (Elater). 



As to the presence of limbs, no trace of pectoral fin or anterior 

 limb has been found. Dean denies the existence of any struc- 

 tures corresponding to either limb, but Woodward figures a 

 supposititious posterior limb in Coccosteus, finding traces of basal 

 bones which may belong to it. 



These monstrous creatures have been considered by Wood- 

 ward and others as mailed Dipnoans, but their singular jaws 

 are quite unlike those of the Dipneusti, and very remote from 

 any structures seen in the ordinary fish. The turtle-like man- 

 dibles seem to be formed of dermal elements, in which there lies 

 little homology to the jaws of a fish and not much more with the 

 jaws of Dipnoan or shark. 



The relations with the Ostracophores are certainly remote, 

 though nothing else seems to be any nearer. They have no 

 affinity with the true Ganoids, to which vaguely limited group 

 many writers have attached them. Nor is there any sure 

 foundation to the view adopted by Woodward, that they are 

 to be considered as armored offshoots of the Dipnoans. 



According to Dean we might as well refer the Arthrodires 

 to the sharks as to the Dipnoans. Dean further observes 

 ("Fishes Living and Fossil"): 



"The puzzling characters of the Arthrodirans do not seem 

 to be lessened by a more definite knowledge of their different 



FIG. 366. Coccosteus cuspidate Agassiz, restored. Lower Devonian. (After 

 Traquair, per Woodward.) 



forms. The tendency, as already noted, seems to be at present 

 to regard the group provisionally as a widely modified offshoot 

 of the primitive Dipnoans, basing this view upon their general 

 structural characters, dermal plates, dentition, autostylism. 

 But only in the latter regard could they have differed more 



