PLATE LXXXIV. 283 



serving exceedingly well as an auxiliary specific cha- 

 racter. There is a considerable amount of irregularity 

 in the size and form of the skeleton spicula ; by far the 

 greatest number are acuate, but the acerate and cylin- 

 drical forms are of frequent occurrence among them. 

 The acuate external defensive spicula are scarcely dis- 

 tinguishable from those of the same form in the skeleton, 



O y 



a slight increase of size being the only difference. The 

 tension spicula of the dermal membrane are felted 

 irregularly together, and their extreme tenuity is in 

 strong contrast with the large and long spicula of the 

 skeleton ; nearly all of them are more or less flexuous. 



