AKD PHYSIOLOGY OF THE SPONGIAD^. 
1113 
so common on all our coasts, Halichondria oculata of the same author, we find an 
abundance of keratose fibre containing spicula deeply imbedded in its substance, but 
not necessarily uniting at their apices ; and the network of the skeleton is not irregular 
as in the first instance, but on the contrary is more or less symmetrically disposed in all 
parts of the sponge. If we take Halichondria suberea of the same authors, we find 
neither network of spicula nor a keratose fibrous structure, but apparently an amorphous 
sarcoid mass containing spicula and membranes, on which the former are dispersed 
without any order or connexion. As we extend our researches among the other British 
species of Fleming’s genus Halichondria, other striking and permanent variations in the 
arrangement of their skeleton-tissues present themselves. Their great difierences in 
structure therefore afibrd ample grounds for the division of the species comprehended 
under HalicJiondria as constituted by Fleming into a series of genera having each for 
its base a separate type of organization ; and as the variations in structural character, 
some of which are mentioned above, are both numerous and strikingly characteristic, I 
propose to limit the genus Halichondria to those species only which agree in their 
organization with H. panicea of Johnston, and to distribute the remaining species in 
other genera, the distinctive characters being in all cases based primarily on the 
different modes of the organization of the skeleton of the animal, and when necessary 
taking in aid such other organic characters as may be found available for the purpose 
of accurate discrimination. I therefore propose to limit the genus Halicho7idria to those 
sponges only that exhibit the following characters. 
Halichondeia, Fleming. 
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, 
which substance, however, 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. Plate LXXIV. fig. 7, and Part II. Plate XXXII. 
figs. I & 5. 
Htalonema, Gray. 
Dr. Geat has characterized this genus in his descriptions of genera of Axiform 
Zoophytes, 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 of the coral, and slightly twisted together like a rope. 
Bark fleshy, granular, strengthened with short cylindrical spicula. Polypiferous cells 
scattered, rather produced, wart-like, with a flat radiated tip.” (Proceedings of the 
7 m 2 
