PLATE XXIV. 



Zone of the Arietites BucMandi, superior. 



Fig. 1. Aegoceras planicosta, Sow. Specimen with ribs and tubercles. 



2. — — — Smaller shell, showing their growth. 



3. — — . — Siphonal area of a small typical shell. 



4. — — — Do. do. showing growth of spines. 



5. — — — This specimen shows that in middle age the 



spines and ribs become relatively less. 



6. — — — Another shell showing curved spines. 



7. — — — ' Do. do. excessive growth of do. 



8. — — — Abnormal growth of ribs and tubercles. 



The three last fossils appear to represent the Am. ziphius, Ziet. t All the specimens 

 are in my collection, and were collected as types out of a considerable number of fossils 

 of the same species at Lyme Regis some years ago, and all are now drawn for the first 

 time. 



