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Show 1867-] DR. BOWERBANK ON HYALONEMA LUSITANICUM. 903 piece mounted in its natural state the structure of the skeleton was distinctly exhibited, exactly resembling, in the forms of its component spicula and in the mode of their arrangement, those of the skeleton of the spongeous base of H. mirabile. In the disintegrated portion I found no less than eight forms of spicula which exist in the basal sponge of H. mirabile, and which I have figured in the plates illustrating m y paper on that species (Proc. Zool. Soc. 1867, p. 18). The spicula found were those represented in Plate V. by figures 2, 4, 6, 7, 8, 9, 18, and those of the skeleton. The only difference between the forms of spicula found in Prof. Bocage's specimen and those from H. mirabile is that those of the former are rather more slender in their proportions, indicating a young and not fully developed state of its organization. The skeleton-spicula of H. lusitanicum are of about the same length as those of H. mirabile, but somewhat less in their diameter, and they have the same malformations of their apices that so commonly occur in those of the last-named species. In truth, the spicula of H. lusitanicum are so identical in form with those of H. mirabile that, without knowing whence they came, it would be impossible for an observer to say from which species they had been obtained. With these slight differences in the organization of the two specimens under consideration, there is little doubt in m y own mind that they belong to one and the same species ; and the slight discrepancies now apparent in the structure of H. lusitanicum will probably disappear when other perfect and more fully developed specimens are hereafter obtained and compared with H. mirabile; and in the consideration of these slight differences of structure the influence of their widely separated localities must also be taken into consideration. Another strong argument against H. lusitanicum being a species distinct from H. mirabile is, that no form of spiculum can be detected in the spongeous base of the former that is not abundantly present in the corresponding parts of the latter. As regards organic structure, there is no true specific distinction existing between them. Their differences amount only to those of development and such as may naturally arise from variations in climate and locality. I have seen the specimen of Hyalonema lusitanicum in the British Museum that was presented by Prof. Bocage, through the sides of the glass tube in which it is carefully preserved. It is 21 \ inches long, and bas 10 inches of the distal portion of the column covered with corium. The specimen is about 2| lines in diameter. There is the same paucity of sand in the crust that is observable in M r . Lee's specimen, described by m e in the Society's 'Proceedings' (1867, p- 350) ; and, as in that case, each osculum is situated in an elongate-oval area, in which, by the aid of a lens of 2 inches focus, the radiating fibres are readily to be seen. The oscula are none of them elevated to the same extent as in the Japanese specimens, but, like those in M r . Lee's one, they project very slightly. The oval areas do not all coalesce at their respective boundaries; in some there is a small space of smooth corium separating them from each other. Having disposed of his new genus Hyalothrix, Dr. Gray proceeds |