1316 
DE. J. S. BOWEEBANK ON THE ANATOMY 
lines of the skeleton passing from the base or centre to the surface, and the 
secondary lines disposed at about right angles to the primary ones. Eeproductive 
organs ovaries, coriaceous and abundantly spiculous. 
All the species are inhabitants of fresh water. The best type of the genus is Spongilla 
■fluviatiHs, Johnston. As an illustration of the form of the skeleton in this genus, see 
the figure of that of Isodictya Normani, Plate LXXIV. fig. 8. 
Suborder IV. Spiculo-fibrous skeletons. Kegularly fibrous. Fibres filled with spicula. 
Besmacidon. 
Raphyrus. 
The spiculo-fibrous skeletons differ from the fibro-spicular ones in this respect. In 
the first the form and proportions of the fibre are dependent on the greater or the less 
development of spicula, and the keratode serves only as a cementing and coating material. 
In the latter the keratode is the primary agent in the formation of the fibre, and the 
spicula the secondary or auxiliary agent only. 
Desmacidox, Bowerbank. 
Halichondria, Johnston. 
Skeleton fibrous, irregularly reticulated. Fibres composed entirely of spicula arranged 
in accordance with the axis of the fibre, cemented together and thinly coated with 
keratode. 
The structure of the skeleton-fibre in this genus readily distinguishes it from all 
others. The form and size of the tissue is entirely dependent on the greater or less 
quantity of spicula present, the keratode serving only as a cementing and coating 
material. Halichondria oegagropila and H. fruticosa, Johnston, are the only two British 
species of the genus known. Part II. Plate XXVII. fig. 10. 
Baphteus, Bowerbank. 
Skeleton fibrous, but not horny. Fibre composed of a dense mass of siliceous spicula 
mixed together without order. 
The structure of this genus is singular. The fibre in the only species with which I 
am acquainted, Raphyrus Griffithsii, is comparatively very coarse, frequently attaining 
the size of a line in diameter near the anastomosing parts, or expanding into a broad 
plate-like form. The spicula composing it are closely thrown together without any 
approach to the longitudinal disposition which prevails in the skeleton of Besmacidon. 
The same absence of definite arrangement obtains in the interstitial membranes, which 
have precisely the mode of structure which characterizes the genus Hymeniacidon, which 
has “ spicula without order, imbedded in irregularly disposed membranous structure.” 
Part II. Plate XXVII. fig. 11. 
