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Show 12 DR. J. S. BOWERBANK ON THE SPONGIADcE. [J G E O D I A INCEQTJALIS, Bowerbank. (Plate II.) Sponge irregularly massive, sessile; surface minutely pitted. Oscula congregated in irregular groups. Pores congregated in minute pits. Dermal membrane obsolete. Skeleton-fasciculi loosely constructed ; spicula rather few in number, inequicylindrical, variable in size. Connecting spicula expando-ternate ; radii short; shafts long, slender, and attenuating. Interstitial membranes spiculous ; tension-spicula inequicylindrical, long and very slender, few in number; retentive spicula attenuato-stellate, very variable in size, number, and degree of attenuation of their radii, comparatively few in number; also cylindro-stellate, very minute, radii numerous and short, very abundant. Ovaria spherical or somewhat oval, slightly depressed. Colour in the dried state cream-white. Hab. Unknown. Examined in the dried state. I received this sponge with other specimens from my late friend Mr. Thomas Ingall in 1861, without any account of its locality. The specimen has every appearance of having been freely floating about iu the sea for some time, as no traces of a basal attachment can be detected on any part of it, and at the part indicated in fig. 18, aa, there is a group of sand-worms which have built their cases upon its surface. I could not detect any portion of a dermal membrane ; but, from the excellent state of preservation of the interstitial structures of the sponge, there is no doubt of its being alive when taken from the sea. Several groups of oscula dispersed over the surface represented in the figure, and especially on the part immediately above the open mouths of the sand-worm-cases at a ; but on the reverse of the figure there are no oscular groups. The oscula are rather small; and, in consequence of the absence of the dermal membrane, the depressed areas of the distal ends of the intermarginal cavities are almost as large as the oscula; but a careful observation soon enables us to discriminate the one from the other. The skeleton-spicula are very loosely combined in the skeleton-fasciculi, and they are rather few in number ; their inequicylindrical form affords an excellent specific character. It is the only Geodia in which I have yet seen that form of skeleton-spiculum; they vary to some extent in size, but the form is constant. The stellate retentive spicula of the largest description vary to a considerable extent; their extremes are well represented by figures 21 and 22, Plate II. In the form represented by fig. 21 the radii are very numerous and acutely conical, while iu that of fig. 22 they have very much more slender radii and comparatively few of them ; but intermediate forms in every degree may be readily found among them. Their average diameter is ^jtj inch. The smaller description, the minute cylindro-stellate ones, are very numerous and much more constant in their forms than the larger ones ; their average diameter is jfe^ inch. The interstitial membranes are rather thickly coated with dark amber-coloured sarcode, and in many parts they are quite crowded with the two descriptions of stellate spicula. |