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Show 1869.] DR. J. S. BOWERBANK ON SILICEO-FIBROUS SPONGES. 97 elevated and margined, dispersed. Pores inconspicuous. Expansile dermal system-dermal membrane pellucid, furnished abundantly with small fusiformi-acerate spicula irregularly dispersed. Retentive spicula fusiformi-cylindrical, short and variable in size. Connecting spicula-apices discoid, irregularly circular or oval, smooth and thin ; margins entire; shafts short and conical. Skeleton-fibres cylindrical, smooth, their free terminations abundantly tuberculated ; tubercles cylindrical, short, terminations hemispherical. Interstitial membranes-tension-spicula fusiformi-acerate, short, rather numerous, dispersed. Gemmules membranous, spherical. Colour light fawn-brown in the dried state. Hab. Island of St. Vincent, West Indies (Rev. Lansdowne Guilding). Examined in the dried condition. This interesting little specimen is in the collection of the British Museum. It was obtained by the Rev. Lansdowne Guilding at the Island of St. Vincent, West Indies. The specimen is a small, unequally developed, cup-shaped sponge ; the margin is nearly oval, with an average diameter of seven-eighths of an inch, and it is about five-eighths of an inch high ; the thickness of the sponge near the margin is about three lines. From its general aspect it would seem that the specimen was a young one in an early stage of development. The oscula are slightly elevated, have a thin margin, and are about one-third of a line in diameter ; they are equally distributed, and are about five or six lines apart, just as they might be expected to appear on a sponge of very much larger dimensions. The pores are dispersed on the outer surface of the cup ; they are not readily detected even in a piece of the dermis when mounted in Canada balsam; they are found in intervals between the discoid plates, which frequently have semilunar notches to afford space for the passage of the inhalant streams. The dermal membrane is very translucent; but the fusiformi-acerate spicula with which it is furnished are so exceedingly numerous that they render the discoid heads of the connecting spicula immediately beneath them perfectly undistinguishable. An average-sized one measured ^ j - inch in length (Plate VI. fig. 12). The retentive spicula are comparatively few in number; they are very much smaller than the tension ones, and although mixed with them are readily distinguished by their fusiformi-cylindrical shape (Plate VI. figs. 13 & 14). The connecting spicula are singular in their form, and very characteristic of the species; the normal form of their discoid heads appears to be nearly circular, but they vary to a very considerable extent to suit the circumstances of their situation. Their margins lap over each other to frequently the extent of one-third or one-half of their diameters, so that they not only form a secure and continuous platform for the support of the dermal membrane, but they also admit of a very considerable extent of lateral expansion and PROC. ZOOL. Soc-1869, No. VII. |
