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Show 20 DR. J. S. BOWERBANK ON HYALONEMA MIRABILE. [Jail. 10, longitudinally and at equal intervals on the internal sides of the cavities. Thus under the last two heads we have a description of forms of siliceous spicula and modes of their disposition in perfect accordance with well-known spongeous organization ; and in truth the whole of the author's descriptions of the Portuguese specimens are strongly in favour of their spongeous nature, both as regards the material of which the spicula are composed, as well as in their mode of disposition on the outer surface of the corium or bark, which is in perfect accordance with the external defensive systems so frequently observed among sponges. No specific characters of Hyalonema lusitanicum are given to distinguish it from LI. mirabile ; and it would not at all surprise me if, upon a further knowledge of the characters of the former, it were to prove to be the same species as the latter; no forms of spicula are given to enable us in the slightest degree to separate the one from the other. Other naturalists have published works on LLyalonema-Prof. John Frederick Brandt of St. Petersburg in 1859, Prof. Max Schultze in 1860, and Dr. Leidy of the United States ; but as I have not seen the specimens described by these authors I shall confine my observations to the type ones of the genus in the British Museum and others which I have had the opportunity of closely examining. The opinions of the authors who have written on these subjects vary considerably from each other ; but none of them, I believe, entertained the idea that Hyalonema was neither more or less than a sponge in all its parts. In 1860, while searching for new forms of spicula and other structural peculiarities of the sponges to assist me in the construction of a systematic nomenclature by which the species might be described, as plants are in botanical science, I became acquainted with the specimens of Hyalonema in the British Museum ; and in the course of a minute examination of the one with the basal mass of sponge I found numerous forms of siliceous spicula which I had not before seen, and which I afterwards figured and described in the ' Philosophical Transactions of the Royal Society of London' for 1862. Figures 3, 4, 5, and 6 in plate 31, and figures 12, 20, 30, 34, 35, 36, 37, and 38 in plate 36, are all from the specimen in the British Museum ; and the result of this examination of the specimen was a strong conviction that the whole of the parts formed but one animal, and that it was truly a sponge. This conviction I published in the third part of m y paper " O n the Anatomy and Physiology of the Spongiadce," in the ' Philosophical Transactions of the Royal Society' for 1862, p. 1113; and as the description of the genus given by Dr. Gray applied only to a part of the animal instead of to the whole of it, I deemed it necessary to enlarge the generic characters so as to embrace the whole of the most important parts of its structure" in the following manner :- " Skeleton an indefinite network of siliceous spicula, composed of |