226 I. IJIMA : HEXACTINELLTDA. I. 



signs of the ledges liaviiig fused together secondarily, occasionally 

 leaving an arch-like or tunnel-like passage underneath. Some- 

 times the elevation surrounds a depression containing a solitary 

 parietal osculum and at other times incloses an irregular valley- 

 like space in which several oscula may lie side hy side. Like 

 the cuff", the ledges are soft and can be easily torn away from 

 the sponge-wall, except in the basal region of the body where 

 they are firm owing to the extensive amalgamation of the mega- 

 scleric elements. 



The parietal oscula are round, up to 3 mm. in diameter, and 

 are surrounded by a narrow oscular membrane as in Eupleclclla. 

 Their distribution must be said to be irregular, being situated 

 3-8 mm. and sometimes even 15 mm. distant from one another. 



The surface of the parietal ledges presents for the most 

 part a rather close-grained texture. However, towards the base 

 of the ledges and over the depressed area around the parietal 

 oscula, there are visible, by the aid of a hand-lens, the usual 

 dermal latticework of a most delicate nature, extending itself close 

 to the oscular edge. Beneath this layer are discernible the 

 variously sized apertures of incurrent canals, measuring up to 

 about 1 mm. across. The same apertures are also exhibited by 

 both the superior and the inferior surfaces of the cuff. 



Leaving the ledges out of consideration, the sponge-wall 

 must in general be said to be thin, except at the much thickened, 

 blindly closed end at the extreme base. In most places the wall 

 does not exceed 2'/._. mm. in thickness. Nevertheless, the entire 



