492 Proceedings of the Royal Irish Academy. 



exterior of the sponge, and the corpuscles succeed one another in a 

 series of arches, as described in Yetulina. 



Professor Zittel differed from Professor Martin as to whether the 

 node of the Anomocladina was hollow or solid, Zittel maintaining that 

 it was solid. What has been said as to the presence of a noval granular 

 space within the centrum of Yetulina bears directly on this point, for 

 during life this appears to be less solid than the rest of the corpuscle, 

 and after death, as solution proceeded, it would become a hollow 

 cavity, as in the case of Yetulina treated with caustic potash. In 

 accordance with this I find hollow centra in the skeleton of Asty- 

 lospongidse. 



It now only remains to redefine the characters of the family : as 

 amended, they run as follows : — 



AlSrOilOCLADINA. 



Skeletal corpuscles, consisting of a massive centrum, from which 

 a variable number of rod-like rays proceed. The rays terminate in 

 expanded ends, which embrace the centra of neighbouring corpuscles, 

 and so produce a firm network. The outer face of the centrum 

 seldom gives rise to rays, but may be provided with spines; it 

 receives the expanded ends of the articulating rays. 



DESCRIPTION OP PLATES III. and IY. 



Plate III. 



Fig. 1. — A specimen of Vetulina stalactites, 0. S., preserved in the Bristol 

 Museum. Seen from above ; a little less than half the natural size. 



Fig. 2. — Idem ; seen from the other side. 



Plate IY. 

 Fig. 1. — Simple cylindrical spicule of Vetulina stalactites. 

 Figs. 2, 3, 4. — Young forms of skeletal corpuscle. 



Figs. 5, 6, 12. — Various forms of fully-formed skeletal corpuscles. Figs. 

 5 to 8 represent the common or staple form of corpuscle, ■with spined heads and 

 rays restricted to one side. Fig. 10. — A corpuscle in which the branched spines 

 are replaced by articulating rays. Figs. 11 and 12. — Irregular coi-puscles, probably 

 aftergrowths. Fig. 12 shows the mode of ai-ticulation of one of these corpuscles 

 with the rays of another of the normal kind. 



The figures of plate iv. were drawn in outline by the camera lucida, figs. 1 to 4, 

 as seen by a Zeiss D, oc. 3 ; and figs. 5 to 12 by a Zeiss D, oc. 2. 



