DESCRIPTION OF THE PLATES. 



Fig. 8. A belemnites of a large size. 



9. A belemnite, the substance of which appears to have been eroded* 



10. A cylindrical belemnite, in which a small linear canal is observable. 



11. A belemnite, terminating gradually in a point. 



12. A belemnite, terminating suddenly in a point. 



13. A fusiform belemnite. 



14. A cylindrical belemnite, with its alveolus. 



15. A conical belemnite, with the concamerated part. 



16. A minute fossil orthoceratite from Sienna. 



17. The same magnified. 



PLATE IX. 



Fig. 1 . A belemnite imbedded in flint. 



2. A baculites from Maestricht. 



3. A spondylolite, a cast formed in the chamber of an ammonite ; a depression on the 



back, marking the situation of the siphuncle. 



4. Part of an ammonite, showing the siphuncle in situ. 



5. The section of an ammonite, showing the course of the siphuncle. 



6. An oval ammonite. 



1. A pyritical ammonite, showing the foliaceous sutures. 



8. An ammonite, possessing a considerable portion of the shell. 



9. The section of an ammonite, showing the sinuous septa. 



PLATE X. 



Fig. 1. Part of a Hamites, nearly straight. 



2. Another specimen, slightly turning. 



3. A large specimen, the hooked form being completed. 



4. A specimen, in which the turn is so made as to show that it could not have termi- 



nated in a spiral. 



5. Another specimen, from the green sand of Wiltshire, showing that it could not have 



been of a spiral form. 



6. | Two views of a fossil shell, resembling the nautilus, but whose genus is not 



7. ) determined. 



