BRITISH SPONGIADjE. 207 



slightest indication of either a bulb or the pedicel for one. 

 II. suberea also frequently simulates the bulbous form of 

 II, feus so exactly as to render it impossible to distinguish 

 the species of either sponge by form alone, but the cha- 

 racters of the spicula, seen with a power of about 200 

 linear, will readily settle the question. 



In its most perfect state of development it has usually a 

 short stout pedestal, and the mass of the sponge assumes 

 the form of a compressed dried fig. I have received this 

 species from the Island of Harris, in the Hebrides, from my 

 friend Captain Thomas, R.N., coating evenly the greater 

 portion of one valve of Pecten opercularis. He states that 

 " when dredged it was two tenths of an inch thick, and had 

 a russet tinge." In its dried condition its thickness 

 scarcely exceeds that of stout writing-paper. Thus in the 

 discrimination of this species very little dependence can 

 be placed in form as a specific character. 



The skeleton spicula of H. feus are mostly acuate, but 

 occasionally they are more or less inclined to assume a 

 spinulate form. The dermal membrane is abundantly sup- 

 plied with minute, slightly curved, cylindrical spicula, having 

 each a bulbous inflation near the middle. The position of 

 this inflation varies considerably ; sometimes it is equidis- 

 tant from the ends of the spiculum, and at others it is about 

 a third of the length of the spiculum from one end. A 

 power of 500 linear is required to show them well. The 

 interstitial membranes are also more sparingly supplied 

 with the same form of spiculum, but varying more in size 

 than those of the dermal membrane ; some of the larger 

 ones are bluntly acerate. No oscula were apparent on any 

 part of the surface of a wet specimen in my possession ; in 

 others, which have been dried, they are few, minute, and 

 scattered, and very rarely attain a diameter of two or three 

 lines. When the dermal membrane is in a fine state of 

 preservation, it is covered with closely packed minute gra- 

 nules, which require a power of not less than 300 linear to 

 be well displayed. These minute organs were also ob- 

 served in the canal membranes of one of my ficoid speci- 

 mens, but I could not see them so satisfactorily in the dermal 



