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Show 22 DR. J. S. BOWERBANK ON HYALONEMA MIRABILE. [Jan. 10, of preservation is in the collection of the Bristol Museum. Numerous other specimens are now known, of which the spiral cloacal column alone has been preserved by the Japanese fishermen who took them ; and of such specimens I have had nineteen in my possession. Of these, five had none of the coriaceous dermis around the spiral column. Three specimens from the collection of m y friend Capt. Charles Tyler had portions of the basal mass of sponge closely adhering to the proximal end of the column, and one of these three has every appearance of having been accidentally withdrawn from the original basal mass of sponge some time previously to its being taken by the Japanese, as there is, about f of an inch above the proximal end of the spiral column, a small bulbous mass of the sponge remaining, nearly an inch in length (Pl. IV. fig. 1). This small mass has secreted a new thin brown dermal membrane, which is continued upward for about an inch, closely surrounding the spiral column. It then throws out ten or twelve of the mammiform oscular bodies in the course of about another inch of its progress upwards, the remainder of the spiral axis being in a denuded state. The membrane surrounding the bulbous mass of sponge and that closely embracing the spiral column above it are continuous and identical in structure, thus affording unmistakeable evidence of their forming parts of one and the same animal. The specimen represented in Fl. IV. fig. 2 has the spiral column enveloped by the corium from its junction with the distal end of the basal sponge for about 2 inches upward, but it does not enter its substance. The dermal membrane of the sponge is entirely wanting. Two of the nineteen specimens had their distal terminations entirely covered by the coriaceous dermis of the column ; and several of them had the thinning off of the proximal extremity of the dermis of the column at the point of its junction with the thin dermal membrane of the distal end of the basal mass of the sponge ; so that between the whole of the specimens there is no part of the entire sponge which is not duly represented. The basal mass of the sponge in the British Museum collection is of a compressed massive form ; it is 5g inches in height, 3| inches in width, and nearly 1| inch in thickness ; the total height, including the cloacal column, is 20 inches. The base of the spiral axis of the cloacal appendage is at or near the base of the sponge ; and it passes thence in a vertical direction through its substance, emerging at its distal extremity. The surface of the spongeous mass has every appearance of having been smooth and even. The great cloacal organ and its oscula are exceedingly interesting in their structure. "While the spiral axis of the cloaca is surrounded by the basal spongeous mass, it has no dermal investment of any kind; but as soon as it emerges from its distal extremity the thin dermal membrane of the sponge is continued over the surface of the column, and gradually thickens in its course upward, until it assumes the form of a stout coriaceous investment, and it then becomes composed of two distinct layers, the outer one being thickly studded with grains of sand and other extraneous substances, which do not |