OF THE SPONGIADyE. 195 



HALICHONDRIA, Fleming. 



Sponge. Skeleton without fibre ; composed of an irregular 

 polyserial network of spicula cemented together by 

 keratode. 



Type, Halichondria panicea, Johnston. 



The anatomical structure of the group included under 

 this genus is distinct and unmistakeable. There is no fibre 

 whatever, the skeleton being formed of spicula collected 

 into bundles of a greater or less number cemented together 

 by keratode, but which substance does not extend beyond 

 the space occupied by the respective bundles ; and when 

 parts of the reticulated skeleton are formed of single series 

 of spicula only, they are simply cemented together at their 

 points, and the reticulated skeleton thus formed has no 

 definite arrangement. 



In some species of the genus the reticnlar character of 

 the skeleton is much more distinct than in others. //. 

 vanicea, although the type of the genus is by no means the 

 best specimen of its character. Fig. 300, Plate XIX, repre- 

 sents a section of //. panicea at right angles to its surface, 

 md Fig. 303, the reticulations supporting the dermal mem- 

 brane, X 108 linear. Fig. 373, Plate XXXV, represents 

 a section at right angles to the surface of a specimen of 

 Halichondria incrustans, Johnston, X 50 linear, a better 

 type of the structural character of the genus than //. 

 panicea. 



HYALONEMA, Gray. 



Dr. Gray has characterised this genus in his descriptions 

 of genera of Axiform Zoophites, or Barked Corals, as 

 " coral subcylindrical, rather attenuated, and immersed in 

 a fixed sponge. Axis in the form of numerous elongated, 

 slender, filiform, siliceous fibres, extending from end to end 



