

134 



THE SPONGES 





such places only a confused mass of spicules. In the superficial region 

 of the sponge, fibres may be distinguished which extend radially to the 



surface. 



The dermal membrane of the upper surface is supported by a reticulum 

 of tangential spiculo-fibres, 70-175 ^ thick, which produce ridges on the 

 surface. Meshes irregularly polygonal or rounded, and varying greatly 

 in size, from 1 mm. to 200 p in diameter (Fig. 6, Plate 21, surface view). 

 The meshes contain, as a rule, no or only a few free spicules. In the 

 larger meshes some free spicules are generally present, and they are 

 frequently combined to form slender tracts, 1 to about 3 spicules thick, 

 which more or less perfectly subdivide the mesh (as in the centre of 

 Fig. 6, Plate 21). The fibres resemble the more compact fibres of the 

 main skeleton. While the dermal reticulum on this surface is in general 

 well developed, there are small areas here and there in which the fibres 

 merge into one another, thus obscuring or obliterating the reticular 



character. 



From the dermal reticulum of the upper surface, single spicules and 

 tufts of spicules everywhere project freely. The latter range from very 

 small tufts including only 2 or 3 spicules to tufts formed by the prolonga- 

 tion of radial fibres of the main skeleton (Fig. 1, Plate 22), or by the 



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oblique prolongation of dermal fibres (Fig. 6, Plate 21), and which at 

 the base have about the thickness of the fibre, 

 abundant, measure 350-500 /x in length, and commonly split distally into 

 branches, each branch including from 1 to 2 or 3 spicules. 



On the under surface a dermal reticulum similar to that of the upper 

 surface is developed in places. Elsewhere such a reticulum is absent, the 

 membrane containing only scattered spicules lying tangentially and crossing 

 at all angles. The non-reticular condition seems to predominate at this 



( 



surface. In the non-reticular regions there may be no projecting spicules, 



The larger tufts are 



Or single spicules, and less often 



the membrane being quite smooth. 



small tufts of 2 or 3 spicules, project. 



Comparative. The species here described resembles some others, assigned 

 to Gellius by recent writers, in that the spicules are in parts of the sponge 

 combined to form spiculo-fibres, which nevertheless are poor in spongin, 

 and do not form a continuous fibrous skeleton as in Gettiodes Ridley. 

 Among such species may especially be mentioned Gellius flagellifer Ridley 

 & Dendy (1887; Lundbeck, 1902). 



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