Plate VIII. 



Arpadites Oabhi Hyatt and Smith, Upper Triassic, California. 



Figs. 1-10, showing development from late larval stage to maturity, 

 and reversion at maturity to some of the ancestral Meekoceras 

 characters. 



Gymnotropites calif ornicus Hyatt and Smith, Upper Triassic, California. 



Figs. 11-13, showing convergence with Discotropites and Eutomo- 

 ceras. 



Beyrichites rotelliformis Meek, Middle Triassic, Nevada. 



Figs. 14-23, showing development from late larval stage, and partial 

 reversion at maturity to the ancestral Meekoceras characters. 

 This species also shows convergence with Ptychites, an entirely 

 different stock. 



All figures from Hyatt and Smith, Triassic Cephalopod Genera of 

 America. 



