DESCRIPTION OF THE PLATES. 
PLATE VII. 
Fig. 1. Part of a hexahedral serpulite. 
2. A v ermiculite in the sandstone of Devonshire. 
3. A specimen of Siliquaria from France. 
4. A spiral serpulite. 
5. A columnar serpulite from Verona. 
6. A polished slab, showing sections of a serpulite externally tetrahedral. 
7. A fossil shell, resembling in many of its characters those of the genus Serpula. 
8. Another fossil shell, resembling in some respects those of Serpula. 
9. A bifurcated tube, resembling that which is represented on a larger scale by Rumptius. 
10. A specimen showing that the siphuncle of the nautilus suffered distension under parti- 
cular circumstances. 
11. A curious fossil, at present referred to the genus Serpula, from Kent. 
12. Part of a nautilite from Brentford, in which is seen the continued siphuncles. 
13. The outline of the back of a nautilite. 
14. An orthoceratites. 
15. A nautilite with sinuous diaphragms. 
16. A nautilite from Yeovil, in which the siphuncle is disposed at the back. 
1 7- The section of an orthoceratite in marble, displaying the siphuncle. 
18. Part of the spiral termination and of the straight portion of a spirulite in red limestone. 
19. Spirulitce in a grey marble, a. the straight part, resembling fig. 14, b. the spiral part, 
as in Fig. 18. 
PLATE VIII. 
Fig. 1. An Hippurites with its operculum. 
2. A cast of a siphunculus of an orthoceratite of a large size. 
3. 1 Show the direction in which the septa of the orthoceratite intersect the siphuncle, 
4. I when it is disposed in the centre or to the side of the septum. 
5. An Hippurites with its supposed siphuncle. 
6. A cast of a siphunculus of an orthoceratite with oblique markings. 
7. A cast of a siphunculus of an orthoceratite, of a large size, with the septa. 
