RAl'fliODESMA. 167 



orifices in the portions of the sponge mounted in 

 Canada balsam ; nor could I under any circumstances 

 detect the pores. When thus mounted for examina- 

 tion the dermal membrane exhibited excellent specific 

 characters. Its reticulated structure was exceedingly 

 well developed. The rete is variable in the number of 

 its component spicula and the areas very variable in 

 form, no two of them appearing to be of the same 

 shape. There were no slender acuate tension spicula 

 in the areas, but the bihamate, retentive spicula were 

 rather abundantly but unequally dispersed, and occa- 

 sionally, but rather rarely, the bidentate, inequi- 

 anchorate, retentive spicula were apparent, but I did 

 not observe in any case two of them together indi- 

 cating a disposition to congregation into rosette- 

 shaped groups. The component spicula of the rete 

 are purely acuate, and are of the same size and form 

 as those of the skeleton fasciculi. The arrangement 

 of the skeleton fasciculi has rather a confused aspect, 

 the bundles varying to a very considerable extent in 

 the number of their component spicula, and crossing 

 each other in every possible direction, and they also 

 vary to some slight extent in length, but in all of them 

 the bases and apices of their spicula are coincident. 

 The confused appearance of the skeleton structure 

 is increased to a considerable extent by the abundance 

 of the long slender tension spicula which are dispersed 

 in all parts of it. The retentive spicula are rather 

 sparingly distributed amid the skeleton structures. 



" There are only two species of British Raphiodesma 

 that might possibly be confounded with the one in 

 course of description R. simplicissimum and R. sor- 

 didum. In the former species the spicula very closely 



