1908.] 



AFRICAN CALCAREOUS SPONGES. 



455 



Skeleton, — The dermal skeleton consists of a thin layer of alate 

 triradiates lying tangentially without orientation ; amongst them 

 are a few quadriradiates, with the apical rays directed inwards, 

 some of very large size. The gastral skeleton consists of a thick 

 layer of large alate quadriradiates, regularly placed with the 

 basal rays directed aborally and the apical rays projecting into 

 the gastral cavity. The skeleton of the central mass of the body- 

 wall between the dermal and gastral layers is a closely packed 

 mass of irregularly placed tri- and quadriradiates. The quadri- 

 radiates, some of which are very large, are mostly ari-anged round 

 the mouths of the excurrent canals, with the apical rays projecting 

 into the canals. The large projecting oxea are bunched into 

 little tufts. The inner ends usually pierce nearly through the 

 wall, and occasionally right through into the gastral cavity. 



But for the presence of the large dermal quadriradiates this 

 sponge would be a typical Leiocandra. 



Text- fig. 104 B. 



Leucilla wasinensis, spicules. X 110. 

 (For explanation of the letters see text below.) 



Spicules (text-fig. 104 A & B). 



The oxea are of one sort : — 



(a) Nearly sti-aight oxea, shai"ply pointed at the inner end, 

 outer end snake-headed. The largest fragment is 2*8 mm. long 

 X 45 /A thick. 



