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Show 1881.] THE SURVEY OF H.M.S. ' ALERT.' 107 latter reason they are with difficulty distinguishable with a lens in this position, though the naked eye is sufficient to make them out in L. antarctica ; the bareness of the stem and of the greater portion of the chief branches is perhaps the most striking superficial point of difference. The species is dedicated to Mr. H. N . Moseley, to whom we owe so much for conclusively determining the affinities of the group to which it belongs. It seems in some respects to connect Errina with Labiopora, representing a transition from the strongly to the feebly labiate character of the chief dactylopores. The comparative absence of prominent dactylopores from the anterior and posterior surfaces of the frond would be an important character, were it not that both this and the condition in which they are universally distributed are found in Errinee in the Museum collection. The colour, too, cannot be appealed to, considering the variations which are shown in this respect by the kindred genus Stylaster and (if E. fissurata, Gray is an Errina, and if the figure by which we know it was taken from a macerated specimen) by Errina itself. XI. SPONGIDA. By STUART O. RIDLEY. (Plates X., XI.) Horny and Siliceous Sponges of Magellan Straits, S. W. Chili, and Atlantic off S. W. Brazil. With regard to the technical nomenclature of the different parts of the Sponges here described, the terms employed are used with the meanings which they bear in Mr. Carter's writings l. In measuring the spicules with the view of stating the typical form and size, the object has been to determine the average largest size of each described form ; in each case at least five of the largest of each form were picked out and measured in order to decide this point. The diameter given for a spicule is the greatest diameter in each case, except that of spinulates or similar forms, where the diameter given is that of the body, not of the head; in the case of spined spicules the base alone of the spines is included.in the measurements. Considerable details have been given under many of the species with regard to the structure of allied forms elsewhere described (chiefly by Bowerbank, Schmidt, and Lamarck). It should be observed that these details are obtained from a fresh and independent study (1) of actual type specimens or slides as far as these could be fixed, in the case of the Bowerbankian species; (2) of the slides and specimens furnished to the Museum by Prof. Schmidt himself in the case of the species described by him; (3) of a collection which undoubtedly represents the type specimens, in the case of Lamarckian species. The type specimen of Ciocalypta tuberculata Carter (see infra), has also been carefully examined. In all these 1 Cf. especially his " Notes Introductory to the Study" &c Ann N TT (4) xvi. pp. 1-40, 126-145, 177-200. " " ' a' |