BRITISH SPONGIAD^l. 323 



in Montagu's series of sponges is not the type of his 

 S. parasitica. It is probable that Montagu may have 

 given the description quoted above, from a specimen of the 

 sponge which I have described under the name of Des- 

 macidon cegagropila, as that species is not only coarse in 

 texture, but also the fibre is frequently fimbriated. 



I have received this species from Burrafirth Caves, Shet- 

 land, from the Rev. A. M. Norman, who says, when alive 

 it is of the richest scarlet colour. Mr. Bean's specimens 

 were parasitic on the branches of a Sertularia; they were 

 very young, and the skeletons only were preserved. In 

 the young state, the symmetrical arrangement of the net- 

 work is generally distinctly demonstrated; the primary 

 lines radiating from its base, and having secondary lines at 

 nearly right angles to them. But in the older specimens 

 this arrangement is not maintained, the whole becoming 

 exceedingly diffused and irregular, and the primary and 

 secondary lines of the skeleton, both being frequently 

 multispiculous, increases the confusion. In the skeleton 

 there are occasionally a few acerate spicula mixed with the 

 acuate ones. 



33. Isodyctia Alderi, Bowerbank. 



Sponge. Encrusting. Surface uneven, hispid. Oscula 

 simple, dispersed. Pores inconspicuous, minute. 

 Dermal membrane pellucid, furnished with dispersed 

 minute bicuspid anchorate spicula. Skeleton. Pri- 

 mary lines multispiculous, stout ; secondary lines 

 variable, frequently multispiculous ; spicula acuate, 

 short, and stout. Interstitial membranes spicula 

 acuate, slender, rarely acerate, slender ; and bicuspid 

 anchorate, minute, dispersed. Sarcode light red, 

 abundant. 



Colour. Alive, faint red. 



Habitat. Bamborough, Northumberland, Mr. Alder. 



Examined. In the dry state. 



