PLATE XVIII. 



Zone of Arieiites Bucklandi. 



Fig. 1. Akgoceras Boucaultianum, d'Orbigny. Lateral view, natural size, from the 



Upper Bucklandi beds of the 

 Scunthorpe ironstone, North-West 

 Lincolnshire, collected by the 

 Bev. J. E. Cross, F.G.S., to whose 

 collection this unique specimen 

 belongs. 



2. — — — This figure represents the shell re- 



duced to one third the natural 

 size, from a specimen in the col- 

 lection of Monsieur Boucault, of 

 Semur. I have seen specimens of 

 this species in the Semur Museum 

 with the shell preserved which 

 measured from twelve to fifteen 

 inches in diameter. 



3. — — — Front view of the same shell to show 



the auxiliary lobes, depressions, 

 and ornamentation on the margins 

 of the siphonal area. 



4. — — — A portion of the foliations of the septa 



drawn by the late Prof. Alcide 

 d'Orbigny, the size of nature. 



