74 BRITISH SPONGIADJE. 



" This sponge is entangled amid the branches of a 

 small specimen of Nullipora polymorplia, coating them 

 rather thinly. Its organic structures are very remark- 

 able, and afford very distinct and striking specific 

 characters, especially those of the derinis. The 

 dermal membrane is very pellucid, and is crowded 

 with the stout, entirely spined tension and defensive 

 spicula; they are all prostrate, thus assuming the 

 character of tension spicula, but their forms and 

 abundant spination render them equally available as 

 defensive organs ; the mode of their disposition has no 

 approximation to order, and I could not detect any 

 of them projected at an angle from the membrane on 

 which they are disposed. The retentive spicula are 

 very minute, but rather numerous, especially in those 

 spaces least furnished with the defensive spicula. The 

 armature of this sponge against either its large or its 

 minute foes is very complete. The largest of two of 

 the bidentate equi-anchorate, retentive spicula mea- 

 sured i 5*0 Q- inch long, the smallest was y^TS" inch, the 

 average length of three was y^j-j inch, and they 

 require a power of about 500 linear to render them 

 distinctly to the eye. The skeleton structure is rather 

 open and cavernous, and the membranes are abun- 

 dantly furnished with their fusiformi-acerate spicula 

 amid which the attenuato-acuate, entirely spined 

 defensive spicula are present in some parts rather 

 sparingly, while in other parts they are more abundant. 

 The minute anchorate, retentive spicula are also rather 

 sparingly disposed on the surfaces of the skeleton 

 membranes. 



" Insignificant as this sponge appears to the unas- 

 sisted eye, it is, by the striking peculiarities of its 



