PLATE LXXXV. 291 



length and Q-^Q-Q in diameter. The interstitial mem- 

 branes are very thin and pellucid. 



This sponge is not a very attractive species, but it 

 is interesting from the irregularity and singularity of its 

 structure. 



I subsequently found among the sponges sent to me 

 by the Rev. A. M. Norman another specimen of this 

 species. It presents the same branching habit as the 

 one first described, and, like it, is parasitical on the 

 slender stems of a small zoophyte combined with 

 branches of Saliconaria farciminoides. The surface of 

 this specimen appears to be in a rather better condition 

 than that of the first one, and a greater number of 

 oscula are seen dispersed on its surface. Internally 

 the structures of the two specimens are in perfect 

 accordance. 



HYMENIACIDON MEDIUS, Bowerbank. 

 Plate LXXXV. 



Sponge sessile, massive, Surface smooth, but 

 slightly corrugated. Oscula simple, dispersed. Pores 

 inconspicuous. Dermal membrane pellucid, abun- 

 dantly spiculous; spicula acuate,or sub-f usiformi acuate, 

 slender, rather less than those of the skeleton, closely 

 and irregularly felted together. Skeleton cavernulous ; 

 spicula sub-fusiformi acuate, long, and slender. 



Colour. In the dry state, ochreous yellow. 



Habitat. Plymouth ; Mr. C. Stewart. 



Examined. In the dried state. 



This sponge was found at Plymouth by Mr. C. 

 Stewart, and was presented by him to my friend the 

 Rev. A. M. Norman. It is based upon three small 

 bouldered pebbles, which it has cemented together. 

 It is of extremely simple structure ; it contains but 

 one form of spiculum. Its nearest allies are Hymeni- 

 acidon mammeata on the one side, and H. plumiger on 

 the other ; but it differs from the former in the total 

 absence of the mammas-form projections on its surface } 



