BRITISH SPONGIADiE. 307 



brane pellucid, aspiculous. Skeleton. Primary and 

 secondary lines unispiculous. Spicula acerate, short 

 and stout. Interstitial membranes. Tension spicula 

 acerate, slender, few in number. 



Colour. Cream white. 



Habitat. Guernsey, Rev. A. M. Norman ; Diamond 

 Grounds, off Hastings, J. S. Bowerbank. 

 Examined. In the fresh state. 



This sponge was obtained by the Rev. A. M. Norman 

 at Guernsey, in 1859. It is two inches long, rather less 

 than one inch broad, and about five lines in thickness. It 

 envelops the branches of a slender species of Fucus, on 

 which it is evident it was based when alive. 



The habit and general external characters of this sponge 

 so closely simulate those of Isodictya lobata, Spongia lobata, 

 Montagu, that without a microscopical examination it would 

 be very difficult, if not impossible, to distinguish the one 

 from the other ; but the difference in the form of the spicula 

 will immediately separate them. The mammae are not 

 uniformly produced ; some of them did not exceed a line in 

 height, while others were three or four lines, but they had 

 all a single terminal osculum. The skeleton is of very 

 delicate structure ; the primary lines being rarely more than 

 unispiculate, and the areas of the network being rarely 

 wider than the length of a single spiculum. The lines of 

 the skeleton are thickly coated with sarcode, so much so as 

 to cause a thin slice of it, when examined in water, to be 

 readily mistaken for a delicate form of Chalina ; but on im- 

 mersion in Canada balsam, the sarcode contracts into a 

 granulated state, and the skeleton assumes the normal form 

 of a true Isodictya. 



Nearly the whole of the dermal membrane was destroyed. 

 In the few fragments remaining I could not detect a single 

 tension spiculum, and very few of them were visible on the 

 interstitial membranes. An adult spiculum of the skeleton 

 measured ^th inch in length. I subsequently obtained a 

 larger specimen of this species, from the Diamond Ground, 



