PLATE LXXVI. 227 



Osciila simple, small, numerous, rarely lai^gc. Poi'cs in- 

 conspicuous. Dermal membrane pellucid, very sparing^ 

 spiculous ; spicula retentive, bidentato, equi-ancliorate, 

 few in number, and rarely, very minute palmate inequi- 

 ancliorate ones. Skeleton diffused and irregular ; 

 primary and secondary lines multispiculous ; spicula 

 subfiecto-acupote, small and slender. Interstitial mem- 

 branes : tension spicula same as tliose of the skeleton, 

 few and irregularly dispersed ; retentive spicula same 

 as in those of the dermal membrane, very few in 

 number. 



Colour. — In the dried state, brown with a tint of 

 green. 



Ilahitat. — Belfast, the late Wm. Thomson, Esq. 



Examined. — In the dried state. 



This sponge entirely covers one valve and_ partially 

 so tlie other of a specimen of Pectcn variiis, its greatest 

 thickness not exceeding three lines. It is the only 

 specimen of the species I have seen, and I am indebted 

 to my kind friend the late Wm. Thompson, Esq., of 

 Belfast, for it. Its locality is probably Belfast 

 Lough. 



The sponge is in an excellent state of preservation. 

 To the unassisted eye, the surface appears indistinctly 

 reticulated from the great abundance of the minute 

 oscula. The hispidation is not visible until a section 

 of the sponge is mounted in Canada balsam, and it is 

 then seen to be produced by the projection of the 

 distal terminations of the primary skeleton lines. 

 Beside the mimerous minute oscula there is a large one 

 nearly three lines in length by two in width on the 

 under side of the projecting mass of the distal margin 

 of the valve which bears the largest mass of the sponge. 

 The dermal membrane does not appear to possess any 

 tension spicula ; occasionally one or two skeleton 

 spicula cross the areas formed by the skeleton tissues 

 immediately beneath, but I could not detect any im- 

 mediately adherent to the inner surface of the dermal 

 membrane, while on many of the clear transparent 



