OF THE SPONGIAD^E. 201 



RAPHYRUS, 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 Desmacidon. The same absence of definite 

 arrangement obtains in the interstitial membranes, which 

 have precisely the mode of structure which characterises 

 the genus Hymeniacidon, which has " spicula without 

 order, imbedded in irregularly disposed membranous 

 structure." 



Fig. 205, Plate XIII, represents a longitudinal section 

 of a small fibre of the skeleton of Raphi/rns Griffithsii, 



L / t*/ 



Bowerbank, showing the irregular disposition of the spicula 

 within it, X 90 linear. 



Suborder V. Compound reticulate skeletons, having the 

 primary reticulations fibro-spiculate, and the interstices 

 filled with a secondary spiculo-reticulate skeleton. 



Diplodemia, Bowerbank. 



This Order forms a connecting structural link between 

 the Orders Silicea and Keratosa. The structure, of the 

 keratose fibre would indicate its place to be in the third 

 suborder of the latter, but the presence of the Halichon- 

 droid secondary skeleton in such force, in conjunction with 

 the irregular spiculated structure of the kerato-fibrous 

 primary skeleton, has induced me to place it among the 



