32G DR. J. S. BOWERBANK ON THE SPONGIAD^E. [Mar. 18, 



at the time, from which it appears to me that the description of the 

 sponge D. setosus in the museum was taken. 



I have a perfect rememhrance that at the time that I was working 

 at the sponges in the museum there was no British species in the 

 collection with which I was not previously well acquainted. I may 

 also add that, although I have since examined numerous species of 

 sponges from the coasts of Dorset, Devon, and Cornwall, I have 

 never seen another specimen of D. setosus from those or any other 

 locality. 



Pachymatisma inconspicua, Bowerbank. (Plate XXXI.) 



Sponge massive, sessile ; surface even, furnished sparingly with 

 small acerate defensive spicula. Oscula unknown. Pores congre- 

 gated. Dermal membrane spiculous ; tension-spicula acerate, small ; 

 retentive spicula attenuato-stellate, small, and very abundant, and 

 cylindro-stellate, minute, and few in number. Skeleton — radial im- 

 mediately beneath the dermal crust for the length of the connecting- 

 spicula, irregular beneath ; spicula subfusiformi-acerate, stout and 

 long. Connecting-spicula attenuato-super-expando-ternate, large 

 and long, with very rarely slender porrecto-ternate or recurvo- 

 ternate spicula. Interstitial membranes abundantly spiculous ; re- 

 tentive spicula acerate, flexuous, very long and slender ; retentive 

 spicula the same as those of the dermal membrane, very numerous. 

 Ovaria spherical, depressed. 



Colour, in the dried state, light fawn. 

 Hub. South Seas (Sir Everard Home). 

 Examined in the dried state. 



This sponge is in the collection of the Royal College of Surgeons, 

 London. It was brought, I believe, from the South Sea by Sir E. 

 Home. It is nearly 3 inches in length. A section from the basal 

 end at right angles to its long axis presented a figure approaching to 

 an oblong of the dimensions of \\ inch by f of an inch. The 

 natural attachment of the sponge is not preserved ; but there is every 

 appearance of its having been a sessile species. 



To the unassisted eye the surface appears smooth ; but by the aid 

 of an inch lens it is seen to be covered with minute puncta, 

 indicating the intermarginal cavities beneath, and a few small acerate 

 defensive spicula are projected for a short distance beyond the 

 surface. When a thin section from the surface is immersed in 

 Canada balsam, and viewed by transmitted light with a power of 

 about 100 linear, the pores are seen to be congregated over the 

 intermarginal cavities, and the pellucid membrane of the areas in 

 which they are situated is furnished with a few small acerate tension- 

 spicula, and it is crowded with the attenuato-stellate retentive 

 spicula ; but without the aid of Canada balsam the latter forms of 

 spicula are invisible amidst the sarcode that lines the inner surface 

 of the membrane. 



The skeleton-structure immediately beneath the dermal crust of 

 the sponge is quite as regularly radiate as that of a Geodia ; and this 



