PLATE LXXIX. 251 



power of 100 linear, the surface is seen bristling with 

 numerous large, external defensive spicula, which are 

 projected to the extent of half or two thirds their 

 length beyond the dermal membrane, to which nume- 

 rous minute grains of sand are attached that obscures 

 it to such a degree as to render exceedingly doubtful 

 the characters derivable from the oscula and pores ; 

 the former appear to be simple, dispersed, and few in 

 number. 



The dermal membrane is translucent, and the large 

 long tension spicula are evenly disposed singly in 

 every possible direction, and it is rarely that two 

 or three are fasciculated together. In the areas 

 formed by this mode of disposition we find the stout, 

 retentive bidentate, equi-auchorate, spicula cemented by 

 the middle of their shafts to the membrane, their an- 

 chorate terminations projected outwards. 



The fasciculi of the skeleton structure are very full 

 of spicula, and do not appear to assume any definite 

 direction in the mode of their disposition. The 

 spicula of the skeleton, as well as those of the dermis, 

 are mostly of a regular acerate form, but occasionally 

 a few stout fusiformi-acerate ones are mingled with 

 them. 



The external defensive spicula are very characteristic 

 in this sponge. They are of two descriptions ; both 

 of them are attenuato-acuate, but differing from each 

 other greatly in size ; the larger ones being very much 

 stouter than a skeleton spiculum, and half as long- 

 again, and having the basal portion for about one 

 fourth of the whole length abundantly spinous, and 

 especially so the extreme basal portion. The smaller 

 form or defensive spiculum is not more than about half 

 the length of a skeleton spiculum, slender in diameter, 

 and is profusely spinous from base to apex. This 

 difference in size and armature between the two forms 

 of defensive organs is a remarkable feature in the 

 structure of the sponge. 



Although this species appears so insignificant as a 



