250 PLATE LXX1X. 



and it was only in the oldest and most mature of the 

 three specimens that I detect them. 



The only sponge that is liable to be hastily con- 

 founded with this species is ffalichondria albula, which 

 presents a very similar dermal arrangement; but a 

 careful examination will soon display the difference in 

 the structure of their spicula and the other differential 

 characters of the two species. 



HYMEDESMIA OCCULTA, Bowerbank. 

 Plate LXXIX. 



Sponge. Parasitical coating. Surface irregular, 

 abundantly hispid. Oscula simple, dispersed. Pores in- 

 conspicuous. Dermal membrane abundantly spiculous ; 

 tension spicula, acerate, large and long, dispersed ; 

 retentive spicula bi- and tridentate equi-anchorate, 

 large and stout, numerous, dispersed. Skeleton fas- 

 ciculi multispiculous ; spicula very numerous, same as 

 those of the dermal membrane, with an admixture of 

 stout fusiformi-acerate ones. External defensive 

 spicula attenuato-acuate ; size various ; large ones 

 basally spined, smaller ones, entirely spined. 



Colour. Milk white in the dried state. 



Habitat. Shetland, ninety-six fathoms ; Rev. A. M. 

 Norman. 



Examined. In the dried state. 



I received this singular little sponge from the Rev. 

 A. M. Norman, who obtained it by dredging in ninety- 

 six fathoms at Shetland. It is based at the distal 

 margin of a fragment of an old Pecten shell, and it 

 occupies a space rather less than the quarter of an inch 

 in length by about the eighth of an inch in breadth ; 

 and it is so like in colour to the fragment of shell on 

 which it is thinly spread, that it is difficult to dis- 

 tinguish it from the shell surface, even with the aid of 

 a lens of two inches focus. 



Viewed as an opaque object by direct light, with a 



