BRITISH SPONGIAD^E. 243 



stance, and when dried they exhibited a very slight amount 

 of corrugation. In the latter condition, the surface is 

 strongly reticulated, very closely resembling that of Hali- 

 chondria panicea ; and in this state, the pores are distinctly 

 apparent with the aid of a two inch lens. With a micro- 

 scopical power of about 100 linear, the dermal membrane 

 is a very interesting object, with its beautifully reticulated 

 structure, abounding in its areas with the open inhalent 

 pores of the sponge. The oscula are small. I could not 

 detect them readily in the living specimens ; but, in the 

 dried condition, they are apparent to the unassisted eye. 

 The strongly reticulated multispiculous skeleton, combined 

 with peculiarities of the dermal membrane, readily "distin- 

 guish this species from others nearly resembling it in ex- 

 ternal form and colour. 



10. Halichondria Thompsoni, Bowerbank. 



Sponge. Coating, surface even. Oscula few, large, slightly 

 elevated. Pores conspicuous. Dermal membrane, 

 simple, pellucid, sparingly furnished with bidentate 

 equi-anchorate retentive spicula. Skeleton. Rete dif- 

 fusive ; spicula sub-fusiformi-acuate, sub-flexuous. 

 Interstitial membranes. Tension spicula acuate, long, 

 and slender. Retentive spicula bidentate equi-ancho- 

 rate. 



Colour. When dry, brown. 

 Locality. Belfast, or Larne Lough. 

 Examined. In the dry state. 



The texture of this sponge, in the dried state, is firm and 

 rigid, and the rete very open and diffusive, the sides of the 

 network being frequently longer than the skeleton spicula, 

 and the interstitial membranes often assuming much of the 

 appearance of those of a Hymeniacidon. The spicula of 

 the skeleton when not fully developed are usually purely 

 acuate, but in their completely developed state they are 



