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Show 96 DR. J. S. BOWERBANK ON SILICEO-FIBROUS SPONGES. [Jan. 28, greatest lateral expansion jfcf inch ; diameter of shaft ^fcs mc^ length of projection of a ray j-fe^ inch ; diameter of a ray yyf-jo inch. The greatest disparity existing between them is not in the size of the shaft, or in the length of the projection of the radii, but in the length of the spiculum and in the various modes of its structure. I have been thus particular in its description because it is a new form of spiculum, and is especially characteristic of the species of the sponge in which it occurs (Plate VI. fig. 8 a). The elongo-attenuato-stellate spicula are comparatively few in number, and very different in their general aspect to the elongo-cylindrical ones. They vary exceedingly in their forms : sometimes they assume the shape of spiculated biternate ones; but generally their long, slender and attenuated radii are projected without any approximation to regularity. An average-sized one measured, length glT inch, length of a ray T T W incn, diameter of shaft j-fe-^ inch (Plate VI. fig. 85). There are also a few short cylindrical spicula, with an irregular inflatiou near the middle ; but this form is probably an undeveloped state of the elongo-cylindro-stellate spiculum. From the collapsed state of the expansile dermal system, no very clear view could be obtained of the investing membrane of the rigid skeleton ; but in sections parallel to the surface, mounted in Canada balsam, small portions of it were occasionally visible; and these appeared to be rather sparingly supplied with the elongo-cylindro- stellate and elongo-attenuato-stellate spicula that are so abundant in the dermal membrane. A few of both these forms of spicula are also found dispersed on the interstitial membranes. The long, slender and flexuous interstitial spicula occur either singly or in bundles of four or five together, and are usually disposed at nearly right angles to the surface, immediately beneath the investing membrane of the rigid skeleton. They are very long and slender, and attenuate to extremely acute terminations. Short, stout fusiformi-acerate spicula in considerable quantities are sometimes found intermixed with the skeleton-fibre, immediately beneath the enveloping membrane of the rigid skeleton; but they are not found in such quantities in all parts of the sponge; amid the deeper portions of the skeleton a few single ones only are occasionally found. A iew short, stout cylindrical spicula were found among the spicula obtained by the dissolution of portions of the sponge iu nitric acid; but these are probably cases of immature development. The sarcode is as abundant in this as in other species of the same genus. Its quantity cannot be correctly appreciated in its dried condition, or when mounted in Canada balsam ; but in wet preparations of portions of the skeleton, when fully expanded by moisture, it is in many cases to be seen completely enveloping the skeleton-fibre, and filling the interstices of its reticulations. DACTYLOCALYX POLYDISCUS, Bowerbank. Sponge irregularly cup-shaped, pedicel short. Surface even; sides of cup thick; margin rounded. Surface even. Oscula slightly |