PLATE IX. 21 



In all the species I have described the pores have 

 been designated as " inconspicuous," and in many of the 

 specimens first examined they were in a closed state 

 and not amenable to the power applied to them. 



In several of the specimens subsequently acquired 

 and examined I have found them in an open condition 

 as represented by fig. 6, Plate X, in P. robusta, and 

 also in P. bulbosa, fig. 2, in the same plate. In a speci- 

 men of P. brevis mounted in Canada balsam they are 

 also rather indistinctly visible. In all these cases they 

 are congregated above the porous areas of the parietes 

 of the fi stulre, and they do not appear to exist on any 

 other portion of those bodies. It will therefore be 

 advisable for the future to consider this arrangement 

 of the pores as the correct description of those organs 

 to be added to the specific descriptions of the species 

 recorded in vol. ii, ' Mon. Brit. Spongiadse.' 



