PLATE XV. 



Fig. 



I, 2. Rhynchonella serrata. Two specimens, nat. size. 



3. „ Bouchardii. A var., with two plaits on the mesial fold, a little 



enlarged. 



4. „ ,, A var., with three plaits, enlarged. 



5. „ ,, A var., with five plaits „ 



6. „ Lycettii, nat. size. 



7. ,, sub-variabilis. A specimen with three plaits on the mesial fold; 



in PI. XVIII, fig. 11, a var. is figured with 

 only two plaits on mesial fold. 



8. 9, 10. ,, variabilis. Three small varieties, with three and four plaits on 



mesial fold : other variations are illustrated in 

 PI. XVI, figs. 1 to 6. 



II. ,, Moorei. A var. (enlarged), with five plaits on mesial fold. 



12. ,, ,, Another var., enlarged. 



13, 14. ,, „ A variation, with seven plaits on mesial fold. 



15. „ spinosa. A specimen, with all its spines attached. 



15°. „ „ A fragment, showing the manner in which the spines 



originate, enlarged. 



16. „ „ A var., with few plaits. 



17. 18. „ „ Beak of two specimens, enlarged, to illustrate the 



foramen and deltidium. 



19. „ „ The largest British specimen. 



20. „ „ A very young shell, enlarged, to show that sometimes 



the plaits bifurcate and intercalate. 



21. „ senticosa, nat. size. 



