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Show 326 DR. J. S. BOWERBANK ON THE SPONGIADcE. [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 remembrance 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 congregated. 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 immediately beneath the dermal crust for the length of the connecting-spicuia, irregular beneath ; spicula subfusiformi-acerate, stout and long. Connecting-spicuia attenuato-super-expando-ternate, large and long, with very rarely slender porrecto-ternate or recurvo-ternate spicula. Interstitial membranes abundantly spiculous ; retentive 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. Hab. 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 1| inch by | 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 iu 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 tbe 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 |
