226 I. IJIMA : HEXACTINELLIDA. I. 



signs of the ledges liaving fused together secondarily, occasionally 

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

 times the elevation surrounds a depression containing a solitary 

 parietal osculura and at other times incloses an irregular valley- 

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

 the cuff", the ledges are soft and can he 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 ronnd, up to 3 mm. in diameter, and 

 are surrounded by a narrow oscular membrane as in Eupleclella. 

 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\'2 nim. in thickness. Nevertheless, the entire 



