192 PLATE LXXII. 



extent in their diameter, some of them being of ex- 

 treme tenuity. The spicula of this species and those 

 of H. consimilis and fl". perlevis are nearly of the same 

 form and proportions ; but in the former of the two 

 species not only is the external form of the sponge 

 distinctly different, but in the dermal membrane, 

 although abundantly spiculous, they are irregularly 

 dispersed instead of being arranged in fasciculi, and in 

 H. perlevis the dermal membrane is aspiculous. 



I subsequently found a second specimen of this spe- 

 cies among the sponges dredged off Guernsey by Mr. 

 Kent. It was about the same size as the type-speci- 

 men, and very closely resembled it in all its external 

 and internal characters, with this difference only, tliat 

 in a piece of the dermal membrane examined one jjor- 

 tion of it very closely resembled that of the type- 

 specimen, while immediately adjoining that spot the 

 fasciculi assumed a reticulated character ; and in 

 another part of the same piece they were indiscrimi- 

 nately felted together. As a precaution to naturalists 

 who attach value to external characters I may mention 

 that the two specimens of this species were mixed with 

 several others of Hymeniacidon reticulatus, and that 

 the two species were so much alike in external charac- 

 ters that I could not separate them without micro- 

 scopical examinations. 



Polymastia oonigeea, Bowerhank. 



Plate LXXII. 



Sponge sessile, coating. Surface strongly hispid. 

 Oscula terminal, inconspicuous, congregated on short, 

 stout, smooth, conical, cloacal fistulas ; apices of the 

 fistulie obtuse ; dermis coriaceous, armed profusely with 

 densely packed, minute fusiformi-spinulate spicula. 

 Pores inconspicuous. Skeleton of cloacal fistulte. 

 Fasciculi polyspiculous, large, and numerous ; spicula 

 super-fusiformi spinulate, basal portions frequently 



