EXPLANATION OF PLATE X. 



Euplectella simplex. F. E. Scb. 



Fig. 1. Youngest specimen. Nat size. 



Fig. 2. Young specimen. Nat. size. 



Fig. 3. Young specimen, cut open. Nat. size. 



Fig. 4. Larger specimen with a well preserved sieve-plate. Nat. size. 



Fig. 4a. Oscular sieve-plate of this specimen seen from above. Nat. size. 



Fig. 5. Lower, somewhat injured end of a larger specimen. Nat. size. 



Fig. 6. A larger specimen, a part of the lateral wall of the body of 



which has been cut out; without sieve-plate. Nat. size. 



Fig. 7. Arrangement of the spicules in a transverse section of the body- 

 wall. The upper side of the figure corresponds to the dermal side of the sponge. 

 X 50. 



Fig. 8. Dermal floricom. x 800. 



Fig. 9. Terminal extension of a branch-ray of a dermal floricom, seen 

 from below. x 800. 



Fig. 10. Branch-ray of a floricom, lateral view. x 800. 



Fig. 11. Graphiocom; the branch-rays of five of the main-rays are broken 

 off. X 300. 



Fig. 12. Lower end of a tetradentate, basal anchor-spicule. x 50. 



Fig. 13. Lower end of an octodentate, basal anchor-spicule. x 300. 



