Plate XI. 



Ussuria Waageni Hyatt and Smith, Lower Triassic, Idaho. 



Figs. 1-14, showing development from larval stage to maturity. A 

 primitive progressive form, showing simple recapitulation of its 

 ancestral history. 



Paranannites aspenensis Hyatt and Smith, Lower Triassic, Idaho. 



Figs. 15-20. Primitive Ammonite, transitional from the Paleozoic 

 Glyphioceratidae to the Mesozoic Ptychitidae, an example of a 

 radicle of a group. 



All figures from Hyatt and Smith, Triassic Cephalopod Genera of 

 America. 



