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Show 124 DR. J. S. BOWERBANK ON SPONGES. [Feb. 13, In his " 1st order, p. 502, Coralliospongia. Sponges hard, coral-like, entirely formed of siliceous spicules anchylosed together by siliceous matter into a network. Mass covered by a thin coat of sarcode when alive." This description is eminently incorrect. No one, I believe, ever yet saw the terminations of spicula united into a network through the morbid action of anchylosis by means of siliceous matter. The material by which they are naturally cemented together is keratode. The* author does not seem to be aware that, although sponge-fibres always anastomose more or less, sponge-spi-cula never do so. And in the description of his first family in this order, Dactylocalycidee, page 505, the author distinctly abnegates his own definition of the order by describing the family thus : - " This beautiful family of sponges is at once known by having the skeleton formed of continuous anastomosing fibres formed of concentric lamina of silica, forming a hard brittle network." Order II. Keratospongia, p. 503. In his definition of this order, the author takes an extremely wide range of skeleton-structure, embracing the true sponges, Dysidea, Chalina, Phakellia, and other genera differing widely in their structural peculiarities. "Subsection 2. Spicular Sponges (Spiculospongice), p. 503. Sponge fleshy, more or less strengthened by fasciculated or scattered siliceous spicules, the bundles being sometimes slightly covered with a thin layer of horny matter. The sarcode is generally abundant; in some few, as Euplectella, it is thin, mucilaginous, and deciduous." This description is decidedly incorrect as regards Euplectella, Owen, as that sponge assuredly has a siliceo-fibrous skeleton, and not a spiculo-fibrous one. See Proc. Zool. Soc. 1867, p. 361. " Order III. Leiosponyia. Sponge-spicules of only one kind, often varying in size and shape in the same species." This is another exceedingly vague description on which to found an order ; and we may reasonably ask whether, if they vary in shape, they can be of only one kind. There are very few species in which the spicules, strictly speaking, would be only of one kind, and in every spiculo-reticulate sponge they are liable to variations in size and shape. The author has placed three families in his version of this order, but in the illustration of each of them he violates his own rules. Thus, in his list of illustrative species of Halichondria (p. 519), he includes H. farinaria and distorta, both of which have two forms of spicula. The same error occurs in his family Polymastidee,-Polymastia bulbosa and radiosa each having two forms, and P. robusta three forms of spicula. The like error is also apparent in his family Clionidee, as, according to Mr. Hancock's description of exotic and other species of Cliona, several of them have at least two forms of spicula in their structure. Order IV. Acanthospongia. This is a most expansive order, as it would embrace every siliceo-spiculous family excepting those included in the author's order 3. The Euplectellaclce are erroneously placed in this order. |