202 PLATE LXXIII. 



tlie rete, composed of numerous spicula, being broad 

 and flat, occupying as much space as the enclosed 

 porous areas. This reticulation obtains over the 

 greater part of the surface, but occasionally there are 

 small patches where the network and its areas are 

 entirely covered over by a dense felting together of 

 spicula of the same size and proportions as those of 

 the rete and of the skeleton. The structures of the 

 dermal surface when thus rendered distinctly visible 

 by immersion in Canada balsam are strikingly charac- 

 teristic of the species; but in almost every other 

 anatomical character of the sponge it might be readily 

 mistaken for Halichondria caduca. The structure of 

 the skeleton very closely resembles that of the last- 

 named species, but on a close comparison it appears to 

 be rather more dense and more abundant in spicula. 

 The skeleton spicula of the two species also agree very 

 closely together, in both form and size, and the only 

 difference seems to be that those of H. edusa are in a 

 slight degree more fusiform than those of H. caduca. 



HALICHONDEIA REGULARIS, Bowerbanlc. 

 Plate LXXIII. 



Sponge massive, sessile. Surface smooth and even. 

 Oscula simple, dispersed, Pores minute, congregated. 

 Dermal membrane aspiculous, translucent. Skeleton. 

 Rete very regular and uniform in its structure; areas 

 triangular or quadrangular unispiculous or bi- 

 spiculous rarely exceeding the width of one spiculum ; 

 spicula acerate short and stout, uniform in size. 



Colour. In the dried state, milk white. 



Habitat. Sark; Mrs. Collings. 



Examined. In the dried state. 



I received this interesting little specimen from my 

 indefatigable friend Mrs. Collings, the lady of the 

 Seigneur of Sark. It is an inch in length, nine lines 

 in breadth, and not quite three lines in thickness. 



