PLATE LVI. 



Zone of Amaltheus spinatus. 



Fig. 1. Amaltheus spinatus. Back view for keel and spines, natural size. My collec- 

 tion. 



2. — — Side view, showing spines. 



3. — — Front view, mouth aperture, and spines, and keel. 



4. — — Lobe-line, magnified. My collection. 



5. — — Front, showing aperture and position of siphuncle. do. 



Zone of Amaltheus margaritatus. 



6 — 14, 19, 20. Amaltheus margaritatus. Shells of different ages showing the evolu- 

 tion of this species. My collection. 



15. — — Type form of a young shell, do. 



Zone of Amaltheus oxynotus. 



16. Aegoceras lacunatum, Buckman. Side view, natural size. My collection. 



17. — — — Siphonal area, showing furrow, natural size. 



18. — — — Front view, do. do. 



