PLATE IV. 



Zone of Arietites Bucklandi. 



Fig. 1. Arietites bisulcatus, Bruguiere = multicostatus, Sowerby. Lateral view, 

 natural size, of a typical specimen from the Lower Lias, near Berkeley. 

 My collection. 



2. Front view of the same, showing the position of the siphuncle. 



3. View of the siphonal area of the same, showing the bisulcations on each side 



of the keel, the tubercles on the ribs, and their angular curvature forwards 

 on the margin of the siphonal area. 



4. Accurate outline of the foliations well seen in this specimen. 



