PLATE LXXIX. 247 



the oye, while those of the other set are projected 

 through the dermal membrane, but the bulbs of both 

 sets are based on the inner surface of the basal 

 membrane. The acerate tension spicula of the spinu- 

 late skeleton spicula are both of them very large and 

 long for so small a species of sponge. The tension 

 spicula are very slender and very acutely terminated, 

 but they frequently exceed -^ inch in length. 



In some of the dermal fasciculi they are too nume- 

 rous to be counted, while in others there are not more 

 than from two to four or five together. The skeleton 

 spicula frequently exceed -^ inch in length ; they are 

 stout and strong in their proportions, and are fre- 

 quently flexuous ; they rarely occur two together on 

 the basal membrane, and from the mode of their 

 attachment they seem to have facile powers of motion 

 when variations in the direction of the shaft becomes 

 necessary. 



The attenuato-spinulate, entirely-spined, defensive 

 spicula are comparatively small ; they rarely exceed 

 Y^-Q inch in length ; they scarcely ever occur together, 

 but are generally disposed at about equal distances from 

 each other. 



The spination of the spherical base of some of these 

 defensive spicula very frequently exhibits a remarkable 

 character in the form of a circular band of spines 

 around its greatest circumference, while the proximal 

 and distal portions of the sphere are entirely without 

 spines. 



In such cases the spination of the shaft of the 

 spiculum does not commence until about half or a whole 

 length of its own diameter above the spherical base, 

 and continues thence more or less to the distal end of 

 the spiculum. The spines are acutely conical, and are 

 projected at right angles to the axis of the spiculum. 



I have a strong suspicion that the coronulated, 

 attenuato-spinulate, defensive spicula are more especially 

 devoted to the external defenses of the sponge, but 

 although I have seen the smooth basal surface and the 



