68 PLATE XXVI. 



surface of a valve of Astarte scotica at a a. Natural 

 size. 



Fig. 6. — A sponge encrusting the greater portion 

 of a small angular pebble, a a being the sponge. 

 Natural size. 



Fig. 7. — One of the large subclavate skeleton and 

 external defensive spicula. X 250 linear. 



Figs. 8 and 9 — Two of the attenuato-clavate, en- 

 tirety-spined internal defensive spicula. X 250 linear. 

 These spicula differ exceedingly in size, some of them 

 being larger than the one represented by fig. 8. 



