PLATE XI. 



Figures 1-11. Spines of Cidaridse; genus Cidaris, natural size. Figs. 5*, 10*, and 11*: Orna- 

 mentation, magnified. (Page 50.) 



12. A spine of Porocidaris, natural size. (Page 50.) 



13. The same, magnified. 



14-23. Spines of Phyllacanthus, natural size. Fig. 16* : Ornamentation, magnified. 

 (Page 50.) 



