158 BRITISH SPONGIAD2E. 



irregular in form, not exceeding an inch in diameter 

 and a quarter of an inch in thickness. Its surface is 

 very uneven and irregular, and its substance open and 

 more or less cavernous. From the state of its under 

 surface it has evidently been removed from a rock or 

 stone by a sharp knife, and a few slender fucoid stems 

 are incorporated in its substance and are adherent to its 

 surface. The oscula are simple, none of them were 

 more than about -^ inch in diameter ; some of them 

 were on the elevated ridges and others in the developed 

 portions of the surface. The dermal membrane is 

 abundantly furnished with spicula. The tension spicula 

 are of two sorts, subfusiformi-acerate or cylindrical 

 and numerous small attenuato-acerate ones inter- 

 mixed with them ; the former are the true dermal ten- 

 sion spicula, while the latter properly appertain to the 

 interstitial membranes, but both descriptions are 

 numerously distributed on the membrane. The former 

 are very irregularly disposed ; on some parts they are 

 numerously dispersed without the slightest approach to 

 order, while in other parts they are more or less fasci- 

 culated and occasionally approach to an irregular reti- 

 culation ; the small attenuato-acerate ones appear 

 always to be irregularly dispersed. The bidentate, 

 equi-anchorate retentive ones are small, but rather 

 stout in their proportions ; a full-sized one measured 

 -QY inch in length ; they require a power of about 

 300 linear to render them distinctly to the eye when 

 in sitit. The bihamate retentive spicula are more 

 numerous than the anchorates. They are rather 

 slender in their proportions ; a full-sized one measured 

 y-g-Q inch in length. 



" The structure of the skeleton appears to be in every 



