140 Eastman — Dvpnoan Affinities of Arthrodires. 



dinary resemblance between them and Arthrodires as regards 

 cranial osteology, to say nothing of other skeletal features? 

 But if modern forms are not directly descended from either 



3 



Fig. 3. — Dinichthyspustutosus Eastrn. Middle Devonian ; Iowa. Restora- 

 tion of the headshield, dorsal aspect, x }£. 



Fig. 4. — Neoce rat odus forsteri Krefft. Dorsal aspect of cranial roof, drawn 

 as if flattened out. Cartilaginous portions dotted, x %. 



of these groups, if their ancestry can be projected backward 

 in imagination to the starting-point from which both of 

 them diverged, then these difficulties become reconciled, real 

 homologies are established between all three groups, and two 

 of them are seen to have elaborated similar cranial patterns. 



