ISODICTYA. 155 



" I received these specimens of this species from my 

 friend the Rev. A. M. Norman for examination; the 

 largest, slightly exceeding an inch in length, was 

 rather less than an inch in diameter ; the other two 

 were each slightly less than half the size of the largest 

 specimen ; they were all embedded amidst the short 

 branches of Nullipora polymorpha. They were dredged 

 in five fathoms, in Westport Bay, Ireland. The oscula 

 are minute, and scarcely visible without the aid of a 

 lens of two inches' focus. The dermal membrane was 

 thickly coated with dark purple sarcode amidst which 

 the tension spicula were embedded rather abundantly ; 

 they were mostly irregularly dispersed, but occasion- 

 ally they were collected in loose flat fasciculi. The 

 spicula are very slender, and their spination requires a 

 power of about 500 linear to render it distinctly to the 

 eye. The retentive spicula are very few in number, 

 and very difficult to detect in situ. The minute bipo- 

 cellate ones are more numerous than the minute 

 inequi-anchorates ; both forms require a power of 

 about 500 linear to render their proportions distinctly 

 visible, and it is only when prepared by boiling in 

 nitric acid and mounting in Canada balsam that they 

 can be distinctly seen. 



" The generic characters of this sponge are very diffi- 

 cult of discrimination ; situated amidst the short stout 

 branches of Nullipora, and penetrated by them in 

 every direction. The normal courses of the primary 

 and secondary lines of the skeleton are very much 

 interfered with by these peculiarities of situation, and 

 to such an extent as in many parts to give the 

 skeleton structures the more irregular reticulated 

 form of a Halichondria ; but notwithstanding these 



