PLATE X. 



Figs. 1-7 are some of the calcareous plates and spines from the plates adjoining the food groove of 

 Plate IX. Fig. 1, after boiling with potash. 



8. Magnified view of the reticulation of some of these calcareous plates (of Fig. 1). 



9. Saddle-like base of the covering plate of a basal pinnule which rides upon the side plates. 



10. The point of one of the covering plates similar to that of which the base is given at Fig. 9. 



11. Spiny and fan-like projections of the base of another covering plate of a basal pinnule. 



12. Magnified view of the reticulation rising from the general surface at the base of the' wings of the 



covering plate of Figs. 9 and 11. 



i 



