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Show 1 9 0 4 .] SPONGES OF THE GENUS LEUCOSOLENIA. 3 5 3 the monaxons, and, as shown by Bowerbank's figures, a great tendency to the production of abnormal forms of triradiates (see text-fig. 95, figg. 18 a-e and 19 a-h, p. 379). Leuconia somesii may, in short, be characterised as an interesting aquarium variety of Leucosolenia variabilis, showing modifications parallel to those described by Bidder for Sycon raphanus *, growing in the Naples Aquarium. Bowerbank himself was struck by the resemblance of this sponge to a Leucosolenia, and particularly to the specimen figured by him in pi. iii. fig. 1, which, as stated above, was actually a specimen of L. variabilis ; he remarks that the only other known British calcareous sponge with which this species is likely to be confounded is Leucosolenia botryoides, but " only in its young and immature state." Leuconia somesii must therefore lie put as a synonym of Haeckel's species variabilis. Enough has been said to justify the criticism made above that Bowerbank did not grasp the real distinctions between the species of his genus Leucosolenia f. It is the great merit of Haeckel, whose name marks the next epoch J in our knowledge of calcareous sponges, that he was the first to understand the great importance of the spicules in specific determinations, and to give descriptions of the species by which they could be recognised clearly. It may be said, in short, that previous to Haeckel's great monograph no species of calcareous sponge was really adequately characterised, and that Haeckel was the first to show how this should be done. Hence, where previous descriptions of a calcareous sponge leave us in doubt as to its identity, Haeckel's determ ination of its characters fixes the application of the name. Had Haeckel carried out his own method with accui-acy and conscientiousness it would not have been necessary for the present paper to be written, but unfortunately this is far from being the case. Of the specimens which I have been able to examine, some have been through Haeckel's hands and have been identified by him, and these show, in many cases, the most extraordinary errors of identification, as will be evident from the descriptions and figures given below. It will be made clear, also, that in two cases at least he founded unnecessary species simply as the result of overlooking spicules in certain specimens which he found to be present in others of the same species. Haeckel's numerous species of Ascons require, one and all, a thorough re-examination, and there can be no doubt that a careful revision would result in * Quart. Journ. Micr. Sci. v. xxxviii. p. 10. t To the well-known monographs of Oscar Sclnnidt [19, 20], more or less contemporary with Bowerbank's writings, further reference is not necessary here, since of Leucosolenia, in the sense used in the present memoir, only two species are described, L. lieberkiihnii, which is not a British form, and L. fabricii, which appears to be a synonym of complicate. X Both of Haeckel's works, the ‘ Prodromus' (1870) and the ‘ Monographic ' (1872), wei'e published at dates between those of the second and third volumes of Bowerbank's ‘ British Spongiadaj; ' but they were not noticed by Bowerbank, and belong in all respects to a subsequent epoch. Of Bowerbank's species, only Leuconia somesii was described after Haeckel's monograph, and is therefore not noticed by the latter. P roc. Z o o l . S o c .-1904, V o l . II. No. XXIII. 23 |
