; 



PLATE XXI. 



Fig. 1. Stegoceras validus, Lambe, prenasal bone ; side view. Natural size. Page 68. 



Fig. 2. The same, inferior aspect. 



Fig. 3. Superior view of another specimen ; natural size. 



Fig. 4. The same ; side view. 



Fig. 5. The same ; inferior view. 



Fig. 6. Stereocephalus tutus, Lambe, symmetrical plate, superior aspect ; one-half the natural size. (Pro. 

 visionally associated with S. tutus). 



Figs. 7 and 8. Similar keeled plates ; one-half the natural size. 



Fig. 9. Siiield of Acipenser aibertensis, Lambe, viewed from abave. Natural size. Page 29. 



