Plate III. 



Lecanites Vogdesi Hyatt and Smith, Middle Triassic, Nevada. 



Figs. 1-3, adult stage, showing persistence in the Goniatite stage, a 

 beginning of arrest of development. This species retains many 

 of the characters of Gephyroceras of the Devonian. 



Nannites Dieneri Hyatt and Smith, Lower Triassic, California. 



Figs. 4-8, adult stage, showing persistence in the Goniatite stage, a 

 beginning of arrest of development, but without reversion. This 

 species retains many of the characters of the group of Gastri- 

 oceras glohulosum of the Carboniferous. 



Gephyroceras uchtense Keyserling, Upper Devonian, Russia. 



Figs. 9-11, adult stage. A primitive radicle, like the ancestor of the 

 Meekoceratidae and Ceratitidae. 



Tinianites acutus Keyserling, Upper Devonian, Russia. 



Figs. 12-14. A primitive Coniatite, a lateral branch of Gephyroceras, 

 and the probable ancestor of the Hungaritidae and of the Sage- 

 ceratidae. 

 Figs. 1-8, from Hyatt and Smith, Triassic Cephalopod Genera of 

 America. 



Figs. 9-12, from E. Holzapfel, Die Cephalopoden des Domanik im 

 siidlichen Timan. Mem. Com. Geol, (St. Petersbourg), Vol. XII, No. 3. 

 1899. 



