FOSSIL CR OSS OP TER YGIANS 



151 



the caudal. In these forms a number of paired gular 

 plates may occur. 



In a closely related genus, EiistJienopteron, also of 



Fig. 151 



Fig. 151. — Gyroptychius. X 4. Old Red Sandstone, Scotland. (After Smith 

 Woodward.) 



Fig. 152. — Osteolepis. X 4. Old Red Sandstone, Scotland. (Restoration 

 from Smith Woodward, after Pander.) 



Devonian age (Fig. 154, A, B), the structure of the basal 

 parts of the unpaired fins is exceedingly interesting ; the 

 radial supports are unfused, while the basals, merged in a 



Fig. 153. — Holoptychius andersonl. 0\d^ Red Sandstone, Scotland. 



single plate, have come into especial relation with the 

 axial skeleton ; the subsequent stage of their differentia- 



