STUDIES ON THE COMPAEATIVE ANATOMY OF SPONGES. 205 



Hence the chamber layer is usually supported solely by the 

 apical rays of quadriradiates, which pierce it from opposite 

 directions. In Amphoriscus cylindrus and A. cyathes- 

 cus (4, 5) we learn from Haeckel that the dermal cortex is 

 composed entirely of the facial rays of quadriradiates, there 

 being no triradiates left. This fact supports the view that the 

 subdermal quadriradiates of the Amphoriscidse are merely modi- 

 fications of the ordinary dermal triradiates, which have de- 

 veloped an apical ray without changing their position. In 

 the case of the subdermal sagittal triradiates of the Heteropidse, 

 on the other hand, the position of the spicules is quite different 

 from that of ordinary dermal triradiates. 



Syculmis. 



The skeleton of Syculmis synapta (5), the only known 

 species of the genus, agrees in the main with that of Ampho- 

 riscus, but is further complicated by the addition of a root- 

 tuft of oxea and anchoring quadriradiates, which is, I believe, 

 without parallel amongst the Calcarea. For further details I 

 must refer the reader to Haeckel's monograph. 



Leucilla(figs. 21, 32). 



In this genus, again, we always find dermal or subdermal 

 quadriradiates with inwardly directed apical rays. These form 

 the most constant feature of the skeleton, the other parts 

 being somewhat variable in different species. A gastral cortex, 

 constructed as in Grantia, is probably always present, and 

 sometimes, as in Leucilla uter (fig. 21) and L. austra- 

 liensis (fig. 22), subgastral sagittal triradiates are still recog- 

 nisable, indicating probably the derivation of the skeleton 

 from the Grantia type. All the triradiates of the dermal 

 cortex may be converted into quadriradiates by the develop- 

 ment of a long inwardly directed apical ray^ as in Leucilla 

 uter (fig. 21); or some of them may still retain their primi- 

 tive triradiate character, as in L. australiensis (fig. 22). 



Grantippsis, or of Polejaeff's Grantia tuberosa (8), which are only 

 slight modifications of the ordinary subgastral sagittal triradiates. 



