PLATE XI. 



Zone of Arielites Turneri. 



Fig. 1. Arietites Bonnardii, d'Orbiyny. Lateral view, natural size, from Lyme Regis, 

 in my collection. 



2. Back view of the siphonal area, showing the oblique rib terminations. 



3. Front view do. do. do. 



Zone of Aegoceras Jamesoni. 



4. Aegoceras Jamesoni, Sowerby. Lateral view, natural size of a good type form 



of this rare species ; the specimen was collected at Hechingen, Wurttemberg. 



5. Back view of siphonal area of the same fossil, showing the rib arches. 



6. Front view do. do. do. My collection. 



