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Show 254 MR. F. J. BELL ON THE ECHINOIDEA. [Mar. 4, Before discussing the relation which Meoma and Brissus hold to another, it is necessary to refer to the subgenus Metalia, under which are included the four species africana (Verrill), maculosa (Gmelin), pectoralis (Lamk.), and sternalis (Lamk.). Of this last-named species there are in the possession of the Museum three examples bearing Dr. Gray's label of Brissus sternalis. Two of them are injured, and are apparently the specimens a and c of Gray's Catalogue; they are about 160 millims. long, and have the vertex considerably elevated. The third specimen, which is well provided with spines, is not more than 100 millims. long; and no part of the abactinal surface is raised above the general level. Prof. Agassiz (p. 145) credits the Museum with specimens from Ptaine's Inlet, Port Essington, Reef Attagor, Luzon, and Osmaga (sic); all these, with the exception of that from Luzon, are young examples of Brissus unicolor. The Luzon example seems, however, to belong to Metalia, and may well be the young of M. sternalis; were it not for the third of Gray's specimens above mentioned it would be impossible to connect this young form with the large examples. Those in the possession of the Museum incline m e to accept Agassiz's account of the changes in this species during growth; but an anxious look-out must be kept for fresh specimens , none have yet been received from the collections made by the 'Challenger' Expedition. Agassiz distinguishes Metalia as a subgenus thus : - " The subgenera Plagionotus and Metalia are united as a single subgenns of Brissus (Metalia), the slight difference in the course of the peripetalous fasciole and the presence of larger tubercles not being sufficient ground, with our present knowledge of the changes due to growth, to warrant retaining them both; and as Plagionotus is already in use among Coleoptera, the subgenus proposed by Gray has been adopted and amended to include Brissidae having a more or less broad, elliptical, or undulating re-entering peripetalous fasciole, and an anterior ambulacral groove." I fear I must take exception to this lucid diagnosis ; not only is the odd anterior ambulacrum of M. maculosa said (p. 599) to be "flush with the test, except towards the ambitus, as it approaches the fasciole, and below it when it is placed in a slight indentation of the test," but a comparison of the "deep " groove of M. sternalis with the slight groove of M. maculosa and M. pectoralis on the one hand, and on the other a comparison of the anterior ambulacrum in Brissus and Meoma, in which at times there are slight indications of depressions, will be sufficient to show that this character is not of more than specific importance, at any rate. I have, indeed, some hopes of showing that this depression of the anterior ambulacrum is a characteristic of the more lately developed forms; but for the present I must be content to remark that in the Brissine series it is only found in forms which, by the elaborate character of their subanal fasciole, indicate their later appearance. This subanal fasciole displays the following arrangements:-In Meoma it is a narrow band, which does not extend beyond the ac- |