PLATE XXVI. 



Zone of Arietites raricostatus. 



Fig. 1. Aegoceras bifertjm, Quenstedt. 



3. — — — 



5. Arietites raricostatus, Zieten. 



6. — — — 



7. — — — 



8. — — — 



9. 10. — — — 



11. — — — 



12. — — — 



13. 



14. 



Side view, natural size. My collection. 



Front view, magnified twice. 



Siphonal area do. 



Side view, showing wing-like ribs, magnified. 



Small shell, natural size. My collection. 



Siphonal view, magnified twice. 



Front do. do. 



Side view, natural size. My collection. 



Front and siphonal views of do. 



Side view, natural size. My collection. 

 Do. do. showing the distance 



of the septa from each other. My 

 collection . 



Front view of same shell. 



Siphonal area of do. 



