272 



CLASSIFICATION OF VERTEBRATES. 



Coccostens appears in the Silurian of Europe, and occurs in the 

 Devonian of Ohio. In the Devonian and carboniferous of Ohio 



FIG. 273. Coccosteus, restored, after Woodward, from Dean. A, articulation 

 of head with trunk ; DB, basalia ; DR, radialia of dorsal fin ; //, haemal arch and 

 spine; MC, lateral line canals; JV, neural arch and notochord; (7, unpaired plate; 

 VB, VR, basalia and radialia of ventral fin. 



also occur some gigantic forms belonging to the genera Dinich- 

 thys, Titanichthys, and Macropetalichthys, the latter genus occur- 

 ring in Germany as well. 



FIG. 274. Dorsal wall of skull of Dinichthys, after Claypole. , ethmoid ; 

 0, exoccipital; F> frontal; M, marginal; N, nasal; P, parietal; PO, postorbital ; 

 PR, preorbital ; S, supraoccipital ; sensory canals dotted. (The homologies of some 

 of the bones with the similarly named elements in other groups is doubtful.) 



ORDER II. SIRENOIDEA. 



Body never with bony plates, usually covered with cycloid 

 scales ; paired fins archipterygial ; pelvis a single median plate. 

 The recent forms are subdivided into MONOPNEUMONIA and 



