PLATE LXXIX. 249 



upon them, from wliicli they could be distinguished 

 only by a microscopical examination. When a small 

 portion of the sponge is mounted in Canada balsam, the 

 striking character of the dermal membrane, with its 

 profusion of comparatively large acerate spinous spicula 

 and the great spinulate ones reposing beneath it, at 

 once leads to a discrimination of the species. In two 

 of the specimens examined, the characters to which I 

 have alluded above were very distinctly rendered to 

 the eye by a power of 108 linear, but in the third 

 specimen, which appears to have been an older sponge, 

 the dermal spicula were so numerous and so closely 

 matted together that it required a power of 183 linear 

 to render them distinctly to the eye. The structures 

 beneath were not visible, and a reversal of the specimen 

 became necessary to obtain a distinct view of them. 



The whole of the structures are very striking and 

 remarkable. The dermal spicula vary to some extent 

 in their structural characters ; many of them are purely 

 acerate, while others are more or less inclined to be 

 fusiformi-acerate ; but all are profusely spinous, and a 

 very considerable number of them are more or less 

 bent angularly at the middle, and at or near the bending 

 point many of them are inflated ; but the latter cha- 

 racter is not so frequently met with as the angulation 

 of the spiculum. In the most mature of the three 

 specimens the fasciculi of the smallest skeleton spicula 

 were very numerous, crossing each other at all angles ; 

 the larger acerate spicula, which are disposed singly or 

 sometimes fasciculated five or six together, were dis- 

 persed in an equally irregular manner, and one in 

 about five or six of them had the inflation at about the 

 middle of the shaft. The great spinulate and the few 

 large acuate spicula are rather abundant, but I never 

 observed them to be fasciculated, nor any of them to 

 be projected through the dermal membrane ; these 

 spicula are very remarkable for their great length and 

 their stout proportions. The internal, attenuato- 

 spinulate, defensive spicula are very few in number. 



