PLATE VII. 



Zone of Arietites Bucklandi. 



Fig. I . Arietites rotiformis, Soiverby. Lateral view of another specimen in the 

 Sowerbyan Collection in the British Museum, entirely denuded of 

 shell, and showing the mould forms of the ribs and tubercles. Natural 

 size. 



Zone of Arietites raricostatus. 



Fig. 2. Arietites raricostatus, Zieten. Lateral view, with much of the shell preserved ; 

 from a fine specimen in the British Museum. Natural size. Locality 

 unknown. 



3. View of the siphon al area of the same shell, showing the keel and the disappearance 



of the ribs after they turn the border. 



4. Front view of the same shell showing like characters. Natural size. 



5. Form of the foliations in this species. 



6. A smaller individual of the same species, in my collection, to show the size of the 



air-chambers and the distance the septa are from each other. 



