194 PLATE LXXII. 



seen to be also very numerous, and their apices are 

 scarcely projected beyond the dermal surface ; but this 

 is not the case when they appear as the sole defensive 

 organs of the fistulas. They are then projected through 

 the dermal membrane for the greater portion of their 

 length, and are extremely numerous, and are closely 

 packed together in such a manner as to resemble wet 

 fur on the skin of an animal membrane, lying in 

 patches without any definite direction. 



The mammiform fistulse rise from a well-defined 

 ring ; up to the outer margin of which they are sur- 

 rounded by the dense crop of large external spicula, 

 which are of the same form and size as those of the 

 skeleton fasciculi of the basal ring, whence they spring. 

 Within this basal ring not a single large spiculum is 

 seen to be projected from the base of the spicula, which 

 to the unassisted eye appears as strikingly smooth as 

 all without the circle appears abundantly and coarsely 

 hispid. This remarkable structural character serves 

 admirably to distinguish this species from its closely 

 allied congeners. 



The fasciculi of the skeleton in the basal mass are ir- 

 regularly dispersed; they are rather loosely constructed, 

 and their distal terminations radiate slightly as they 

 approach the dermis, through which they are projected, 

 thus forming the abundant hispidation of the basal 

 dermal surface. 



The skeleton fasciculi of the cloaca! fistulse are large 

 and numerous, the interspaces between them being 

 not more than about half the width of one of the bun- 

 dles. 



The spicula, of which all the parts of the skeleton 

 are formed, are large and long ; the shaft of the spi- 

 culum is strikingly fusiform, but the spinulation is by 

 no means strongly produced. Their most remarkable 

 character is, that the greater portion of them are bi- 

 or tri-spinulate, and in some cases the spinulate infla- 

 tions on the basal portion of the shaft are as many as 

 four or five at nearly equal distances from each other. 



