BRITISH SPONCHAD.i:. 381 



5. Isodictya varians, Bowerbank. 



Halicuondria cinerea, Johiidon. 



Sponge. Encrusting. Surface smooth and even. Oscula 

 simple, minute. Pores inconspicuous. Dermal mem- 

 brane spiculous, reticulated ; rete unispicular ; spicula 

 acerate, rather less in diameter than those of the skele- 

 ton. Skeleton : reticulations unispiculous, rarely 

 exceeding the length or width of one spiculum ; spi- 

 cula sub-fusiformi-acerate, short and stout ; with a 

 few short and stout acuate and cylindrical ones inter- 

 mixed with them. Interstitial membranes. Spicula 

 sub-fusiformi acerate, rather slender. 



Colour. Light gray, in the dried state. 

 Habitat. Shetland, Mr. Barlee. 

 Examined. In the dried state. 



This sponge is in the Johnstonian collection of British 

 Sponges in the British Museum. It is marked 17 E , and 

 labelled Halichondria cinerea, and is arranged on the same 

 board with three other species of the genus Isodictya of 

 this work. It surrounds two adjoining branches of a small 

 Fucus, forming two parallel and united cylinders of sponge, 

 an inch in length and seven lines in width, and varying in 

 thickness from one to two lines. 



The dermal membrane is nearly entirely destroyed, but 

 the reticulated structure with which it is furnished is in 

 perfect preservation. The network is unispiculous, and the 

 areas either four or five sided, rarely triangular, each side 

 consisting of a single spiculum. The skeleton is very 

 regular in its structure ; the normal form of its spicula is 

 sub-fusiformi-acerate ; with these there are frequently, but 

 irregularly combined in its structure, the abnormal acuate 

 and short stout cylindrical spicula ; they occur in both the 

 primary and secondary portions of the network, hut more 



