26 DR. J. S. BOWERBANK ON CEYLONESE SPONGES. [Jan. 7, 



The normal form is that of a thin, more or less expanded cup, some- 

 times cleft at the edges, as in the one figured ; in others the margin 

 is quite perfect ; and in all the pedicle is very short and slightly ex- 

 panded, and the substance of the parietes of the sponge is equally 

 thin and delicate, so thin that if it be held up to the light the 

 radial structures of the primary lines of the skeleton may be readily 

 seen by the aid of a lens of two inches focus ; the margin of the cup 

 is very little thicker than a stout sheet of paper, and even near the 

 base it rarely exceeds a line in thickness. 



The oscula are dispersed on the inner surface of the cup, at nearly 

 equal distances from each other. The circular ones rarely exceed 

 half a line in diameter. In many cases, instead of the usual circular 

 form, they consist of three or four narrow shallow lines radiating from 

 a centre. This variation in their form is remarkable, and I do not 

 recollect ever having seen the like of it before. 



I could not detect the pores on any of the portions of the outer 

 or inhalant surface of the sponges which were examined. The dermal 

 membrane is very thin and delicate in its structure. 



The primary lines of the skeleton are very much stouter than the 

 secondary ones. They do not radiate in strictly straight lines, and 

 frequently meander to some extent in their course ; but their general 

 direction is distinctly in lines radiating from the central basal attach- 

 ment of the sponge. 



Mr. Holdsworth, in a letter to me descriptive of its locality, states 

 as follows : — " Spongionella is only found on the 9-fathom line of 

 the large pearl-bank. It is attached to pieces of dead coral or 

 stones. When alive it is of a dark brown ; and when taken out of 

 the water it looks exactly like dirty wet leather. If you soak a bit 

 of one of the dark specimens you will see it with as nearly as pos- 

 sible the original appearance. 



" This sponge is so strictly confined to the locality above mentioned, 

 that its discovery by the divers is considered the strongest evidence 

 that the outer part of the bank has been reached. 



" I should mention that the banks, strictly speaking, are only beds 

 of gravel, stones, and dead shells in the midst of the general sea- 

 bottom of fine white sand, and the water is as deep over them as in 

 the neighbourhood." 



Dysidea conica, Bowerbank. (Plate VI.) 



Sponge conical, pedicelled ; surface covered with small acutely 

 conical papillae. Oscula simple, large, dispersed. Pores inconspi- 

 cuous. Dermal membrane thin, pellucid, abundantly arenulous. 

 Skeleton fibro-membranous, unsymmetrical, abundantly arenulous. 

 Interstitial membranes aspiculous. 



Colour in the living and dead state — pedestal light grey, conical 

 mass dark purple. 



Ilab. Large Pearl-bank, Ceylon, in 8 fathoms (Mr. Holdsivorth). 

 Examined from spirit, as it came from the sea. 



• This interesting little species of Dysidea was dredged up by Mr. 



