194 A MONOGRAPH OP THE 



the sponge, from the proximal to the distal extremity, and 

 occasionally there were short portions of its length which 

 were not entirely closed. 



These sutures appear to me to be the results of the parasi- 

 tical habit of the species, as in one of them I fonnd the 

 remains of a tubular, horny Zoophyte at the base, and at very 

 near the apex of the sponge, immediately on the line of the 

 longitudinal suture, evidently extending from the base to the 

 j)oint near the apex where the Zoophyte emerged from the 

 sponge, and in another specimen small portions of the 

 included bodies projected occasionally from its surface, but 

 were broken close off, apparently after the sponge had been 

 dried. 



In two of the specimens also the impressions of the 

 included Fuci or Zoophytes were distinctly apparent on the 

 surface of the sponges. Mr. Bean has also a series of 

 specimens similar to those I have described, which were 

 obtained from Mr. Cullen, who informed me that the whole 

 of them were dredged by the trawlers at the Dogger Bank, 

 from which locality it is very probable that the type specimen 

 of Halichondria virgidtosa (Johnston) in Mr. Bean's cabinet 

 was obtained. 



Three of my specimens had their basal attachments perfect, 

 and in each the substance from which they sprung was a 

 dentalium, and in each case there was not the slightest 

 tendency to lateral expansion of their bases ; and the general 

 habit was evidently that of closely embracing and lapping, as 

 it were, their supporters, entirely within their substance. 

 Their course was directly upwards, and not the slightest 

 disposition to branching was evinced by either of them, not 

 even as in the one where the included horny Zoophyte emerged 

 from its broadside. 



The dermal membrane is thin and pellucid, and crowded 

 with nlinute inflato-cylindrical spicula, which are thickly 

 matted together. The inflation in these spicula is not always 

 dt the middle of the shaft ; in this respect it varies consider- 

 ably, in some approaching very nearly one of the terminations 

 of the spiculum. Although so abundant in the dermal mem- 

 brane, they are of rare occurrence in the interstitial ones. 



