285 



narrower tbat the aphodi. The flagellated chambers are ellipsoid. 



The skeleton consists chiefly of radiatiug buudles of oxeas. The 

 nearer to the cortex , the more plagiotriaenes appear. The bundies 

 traverse the cortex; here the plagiotriaenes prevail. There is no 

 special cortical skeleton ; a dermal skeleton is formed by one or 

 more layers of chiasters. The honeycomb appearance of sonie 

 specimens is due to the fact that between the bundies of mega- 

 scleres the cortex remains thinner and thus forms sraall depres- 

 sions. lu specimens where the growth of the cortex is equal, no 

 such depressious are visible and the sponge-surface can then even 

 look quite plane. 



Sp ie u les. Oxea. Stout, straight or very slightly curved , sharply 

 poiuted ; the extremities not unfrequently teat-like. 



Plagiotriaene. Stout; cladi short, conical, straight or abruptly 

 curved; angle Cp on an average 120°, but varying between 110° 

 and 140°. 



Oxyaster. Actines as a rule cylindrical , blunt. 



Chiaister. Resembling the parenchymal oxyasters , but smaller. 



Microxea. Not frequent, sometimes very rare (or absent?). 



PoeciUastra fragilis n. sp. 



The shape is that of a flat cake , slightly curved. The convex 

 side bears the stomas, the concave side the procts. The latter 

 are larger than the former and surrounded by a light yellow vvall 

 or ring. The colour is dirty yellow or buff. 



A transverse section does not show large (excurrent) canals ; 

 the substance resembles crumb of bread. Under the dermis there 

 is a system of subdermal cavities , which communicate with wide 

 lacunae; frotu these start the ramifying incurr§nt canals. Prosodi 

 short , not very narrow. Aphodi wider than the prosodi. Flagel- 

 lated chambers ellipsoid. The exhalant canals termiuate into 

 simple procts. 



The dermal skeleton consists of some layers of microxeas , and 

 some few oxeas, lying parallel to the surface, centrif ugal from 



