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Show 86 DR. J. S. BOWERBANK ON SILICEO-FIBROUS SPONGES. [Jail. 28, form from circular to oval, and occasionally they are nearly oblong. They are protected from the incursions of minute annelids and other enemies by the projection into their areas of the furcated terminations of the skeleton-fibres of the surface-tissues (Plate IV. fig. 2). This beautiful mode of defence is very characteristic of the species, and is an excellent substitute for the usual defensive spicula in such organs. Beside this mode of defence, the dermal surface is furnished rather abundantly with long slender flexuous spicula, which pass over the inhalant areas in various directions. The oscular surface of the sponge is not furnished with the same minute slender acerate spicula that abound on the inhalant one, but the whole of the former surface is protected by a modification of the style of defence that is so beautifully exhibited on the margins of the inhalant areas. The oscular membrane which closes that organ and the slightly elevated ring whence it proceeds have not the same furcated defences that are so abundant at the margins of the inhalant areas ; but as we focus downward through the orifice towards the surface of the rigid skeleton of the sponge, we occasionally observe some of the furcated defences projecting from the parietes of the cavities. The oscular membranes at several of these orifices were in a semicontracted state ; numerous minute grains of sand were scattered on their external surfaces, but no spicula were apparent in any of the membranes. In one of them the margin was in a very perfect condition, slightly thickened; and the membrane exhibited faint concentric lines of contraction (Plate IV. fig. 3). The dermal membrane is pellucid, and is furnished with a fine but very irregular network or stratum of slender siliceous fibres, their siliceous structure being well characterized by the frequency of their fractures at right angles to their axes ; they do not appear to anastomose, but to overlie each other without any approach to symmetry in the mode of their disposition. Plate IV. fig. 4 represents a small portion of this tissue beneath a power of 308 linear. The skeleton-tissue is exceedingly irregular and intricate. The fibres of which it is composed are more or less compressed; they are quite smooth, but frequently throw off short branches which terminate with crowded masses of minute ramifications of siliceous structure. In July 1861, when I first saw this sponge in the collection of the Jardin des Plantes at Paris, the late Professor Valenciennes told me that he had not yet described it; and on the occasion of m y last visit to Paris, in M a y 1868,1 could not learn that he had subsequently done so. I am therefore quite ignorant of the characters he would have assigned to his genus Coscinospongia; but as it agrees in the structure of its skeleton with Stutchbury's previously established Dactylocalyx, I have assigned it to that genus accordingly. DACTYLOCALYX MCANDREWII, Bowerbank. MacAndrewia azorica, Gray, P. Z. S. 1859, p. 438, plate xv. Sponge pedicelled, sinuously cup-shaped. Surface even or slightly undulating. Oscula small, evenly dispersed on the inner or |
