PLATE X. 



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

 Plate IX. Fig. 1, after hoiling 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. 

 1 1 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. 



