PLATE XCI. 341 



could not detect the pores in specimens of the dermis 

 when mounted in Canada balsam, all of them being in 

 a closed condition. The nearest alliance with the 

 known species of the first section of our British Hali- 

 chondria is with //. regularis. The spicula of the two 

 species are as nearly alike in size and proportions as 

 possible ; but this is their only approximation to each 

 other. In their other characters they differ to a 

 considerable extent. The colour of H. regularis, in the 

 dried state, is milk-white, while that of H. Mclntoshii 

 is nut-brown; and in the latter, when viewed by 

 direct light with a power of 50 linear, the pores 

 appear to be irregularly dispersed, while in the former, 

 under the same circumstances, they are seen to be 

 congregated in minute areas. Another important 

 difference is, that while the skeleton rete of H. 

 regularis is remarkable for its symmetry, that of 

 H. Mclntoshii is irregular to a very considerable 

 extent, and it does not possess the distinct unispicu- 

 lous structure that prevails in the skeleton in If. 

 regularis. The skeleton is very irregular in its struc- 

 ture and by far the greater part of it is unispiculous, 

 occasionally the rete is composed of two or three 

 spicula, but these stouter portions rarely extend for 

 more than the length of three or four spicula. 



I have named this species after its discoverer, Dr. 

 Mclntosh, whose works on the British Annelida, and 

 other branches of natural history, are so well known 

 and so highly appreciated among naturalists. 



DYSIDEA CORIACEA, BowerbanJe. 

 PLATE XCI. 



Sponge massive, sessile. Surface slightly asperated. 

 Oscula simple, dispersed. Pores inconspicuous. 

 Dermal membrane coriaceous, rather stout, aspiculous. 

 Skeleton. Unsymmetrical ; fibres large and fistulous ; 



