ON SOME JAPANESE CALCAREOUS SPONGES. 35 



They open into the gastral cavity by apertures of 150-250 /^ dia- 

 meter, separated by interspaces of 50-250 /^. 



The flagellate chambers, densely arranged between inhalant 

 and exhalant canals, are generally of an oval shape, about 80- 

 150// in the shorter diameter. Some of them, especially those in 

 the periphery of the sponge, may be of a more or less elongate 

 shape and are arranged radially around the exhalant canal, thus 

 suggesting the sylleibid condition. 



Skeleton (PI. II., fig. 17). 



The dermal skeleton is composed of microxea, triradiates, 

 large oxea and the paired rays of subdermal pseudosagittal tri- 

 radiates. Nearly all tlie microxea stand vertically to the dermal 

 surface. Those at the oscular margin stand out parallel with the 

 long axis of the sponge. The trii'adiates are placed tangentially 

 in a few layers, with the basal ray pointing more or less down- 

 wards. The large oxea generally run longitudinally, covering all 

 over the sponge surface. 



The tubar skeleton is of the inarticulate type, being composed 

 of the centripetal rays of subdermal pseudosagittal triradiates and 

 of the centrifugal rays of subgastral sagittal triradiates. The ends 

 of the rays mentioned usually reach beyond the middle of the 

 w^all, and there exist between them no intermediate spicules in- 

 dicative of an articulate skeleton. 



The gastral skeleton is thinner than the dermal and contains 

 tlie paired rays of subgastral triradiates as well as large oxea and 

 quadriradiates. The oxea nearly resemble those of the dermal 

 cortex, but are much less numerous and somewhat more irregularly 

 placed. The quadriradiates are slender-rayed and fairly large in 



