BRITISH SPONGIAD^I. 257 



slightly dilated, and frequently exhibit very faint traces of 

 incipient spination, requiring a linear power of about 700 

 to render it visible. These spicula are about the same 

 length as those of the skeleton, but not above half or two 

 thirds of their diameter. Their mode of disposition in the 

 dermal membrane is very irregular; sometimes they are 

 congregated inconsiderable numbers in broad flat fasciculi, 

 in others, the bundle consists of two or three spicula only, 

 and single spiculum are also abundantly dispersed, lying in 

 every direction in the spaces between the fasciculi. The 

 long slender tension spicula are faintly visible in a specimen 

 mounted in Canada balsam ; they are rather numerous, 

 and are about equally dispersed in all parts of the mem- 

 brane, but in a specimen mounted in water they are not 

 visible. The same may be said of the retentive spicula 

 which are very few in number. The tension spicula are so 

 extremely attenuated that they require a power of at least 

 700 linear to render the form of their terminations distinctly 

 visible; thev are abundant in the interstitial membranes, 

 while the retentive spicula are so few in number as to be 

 very rarely detected. The spination of the skeleton spicula 

 is by no means regular ; sometimes the spines are thinly 

 distributed over the whole of the spiculum, in others they 

 are basally and apically spinous, and occasionally they are 

 only basally spinous, and in all they are in so incipient a 

 state as to be nearly invisible when immersed in thesarcode, 

 even when mounted in Canada balsam, and it is only after 

 being separated from the tissues by the aid of nitric acid 

 that their characters are rendered distinctly visible. 



There are only two sponges with which this species may 

 probably be confounded, //. Ingalli and H. Pattersoni. In 

 the former species the skeleton spicula, although of the 

 same form are very much smaller and more slender than in 

 H. pidchella, and in the latter they are much larger, and 

 have their spination more boldly produced than in the 

 sponge under consideration. The total absence also of 

 anchorate spicula in H. pukhella serves also to render its 

 separation more complete. 



17 



