BRITISH SPONGIADiE. 97 



large; spicula frequently with one or two extra infla- 

 tions near the basal one. Interstitial membranes. 

 Tension spicula abundant, the same in form as the 

 dermal ones. 



Colour. Dried, light gray. 



Habitat. Shetland, Deep sea, Mr. Barlee, and Rev. 

 A. M. Norman, 1863 \ Unst, Shetland, Mr. C. W. Peach, 

 1864. 



Examined. In the dried state. 



The first specimens I received of this sponge were from 

 my friend the late Mr. Barlee, who dredged them, I believe, 

 in about 70 fathoms, off Shetland. 



The greatest diameter of the large specimen is one 

 inch, that of the smaller one three quarters of an inch. 

 The height of the large specimen is about a quarter of an 

 inch, and its greatest thickness about one third of a line. 

 There is a considerable amount of extraneous matter de- 

 posited on the upper or convex surface of each of the 

 sponges ; and the concave, or underside of each, appears 

 perfectly clear from such impurities. The only attachment 

 in both of these specimens is to the small pebble imbedded 

 in its centre, and the species is evidently not stationary, as 

 in the larger specimen, with the concave surface downward, 

 the central stone does not touch the plane surface on which 

 its marginal fringe rests, and the under surface of the 

 pebble in each is partially covered by a thin stratum of 

 spongeous matter. The upper surface of the pebble in 

 both is entirely covered by the dermal tissue of the 

 sponge. This accordance in habit seems to indicate that 

 the natural position is with the concave surface downward, 

 and its freedom from impurities on that surface is the 

 natural result of the action of the excurrent streams from 

 the oscula which abound at the margin of the concave 

 surface of the sponge. The habit of the sponge of in- 

 cluding a small pebble in its centre, apparently as ballast, 

 is very remarkable, and this is the only case in which there 



7 



