Plate VII. 



Meekoceras 7nusJihachanum White, Lower Triassic, Idaho, 



Figs. 1-5, adult stages, showing development towards Ceratites. 



Meekoceras gracilitatis White, Lower Triassic, Idaho. 



Figs, 6-12, showing development from early stage to maturity. 



Both species are primitive forms, intermediate between the Goniatite 

 ancestry and the Ceratitic posterity. Both are intermediate in characters 

 between the Paleozoic and the Mesozoic types. 



All figures are from Hyatt and Smith, Triassic Cephalopod Genera 

 of America. 



