PLATE LXXIV. 217 



visible on any part of the margin of the sponge. The 

 specimen as it is might be readily mistaken for a por- 

 tion of Isodictya infundibuliformis by a casual observer, 

 but its anatomical structure at once separates it from 

 that species. 



The most certain and striking specific character is 

 found in its dermal membrane. When a portion of it 

 is mounted in Canada balsam and viewed by trans- 

 mitted light with a power of about 100 linear, it is seen 

 to be profusely spiculous ; but the spicula are not 

 indiscriminately felted together without any approxi- 

 mation to order, but they are collected into short fasci- 

 culi, each composed of from two or three to seven or 

 eight spicula parallel to each other. The flat bundles 

 cross each other in an irregular manner at various 

 angles, and numerous single spicula are irregularly 

 dispersed among them, the tissue as a whole having 

 the appearance of a very irregularly made mat of 

 short, flat, bundles of spicula. When viewed in the 

 dried state by the aid of a hand lens, the dermal sur- 

 face has much the same minutely reticulated appear- 

 ance that is so well known in dried specimens of Hali- 

 chondria panicea. 



The form and size of the dermal spicula and those of 

 the skeleton are exactly the same. 



In the dried condition the sponge is firm and strong, 

 and of nearly a white colour. 



