DUSEIDEIA FRAGILIS, Johnston. 



Spongia fragilis, Montague. 

 (Plate vi. fig. 11). 



Duseideia fragilis. Form massive, variable, sessile. Surface exas- 

 perated, of a dull ochreous yellow colour. Excurrent canals few, 

 large. Fibre of the skeleton rigid, coarsely reticulated, rugose, with 

 numerous grains of sand imbedded in their substance, or tubular, with 

 few or no grains imbedded in their structure. 



Spicula of the skeleton variable in size and form, imbedded within 

 or attached to the outer surface of the fibre. 



This species is the Spongia fragilis of Montague, who has described 

 and figured it in his paper on British sponges, published in the first 

 volume of the * Memoirs of the Wernerian Society.' The specific de- 

 scription of that author is as follows. — " Spongia fragilis. Fragile, 

 friable, coarsely reticulated ; the fibres rugose, as if covered with mi- 

 nute sand." The figure, although coarsely executed, is characteristic, 

 and is evidently that of the skeleton only ; and from the subsequent 

 portions of the description it would appear that the author had seen 

 no other specimen than the one he describes. 



The specimen represented by figure 11, I found attached to the 

 Thatcher rock, near Torquay ; and it was undoubtedly alive when I 

 removed it from the rock. I have since procured numerous speci- 

 mens from among the sea-weeds cast up on the beach at Brighton, 

 the greater portion merely skeletons, but others were in various stages 

 of decomposition, and some few in a sufficiently fresh and perfect 

 state to allow of their being proved to be the same species as the 

 Torquay specimen. Under these circumstances I have thought it ad- 

 visable to add to and somewhat modify the original description of 

 Montague, but I have adhered to it as closely as possible. Thus 

 Montague has described it as fragile, while, in the majority of cases, 

 the fibre is comparatively strong and rigid, from the great quantity of 

 sand imbedded within it. He has also described it as friable, but as 

 this character applies only to the skeleton in the dry state, it is better 

 omitted as unnatural. The form of this species is exceedingly varia- 

 ble. In its young state, as represented in figure 11, it is spread over 

 the surface to which it is attached, as if it were a coating sponge ; but 

 when fully developed it rises to the height of two or three inches, and 

 has a tendency to assume a thickened fan-shaped or compressed form ; 

 and the base is usually twice or thrice as long as it is broad, as if this 

 were the natural mode of its development. 



