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Show 252 MR. F. J. BELL ON THE ECHINOIDEA. [Mar. 4, tion within the limits allowed by inheritance, and the development useful variations into fixed and definite differences. The only criteria which we can apply to problems of this character seem to be the observation (1) of what obtains in allied forms, and (2) of what obtains in forms living under somewhat similar conditions. The variations which appear to occur in Metalia sternalis during growth, and the varieties of Diadema setosum, are to be cited as supporting examples of the first, as are the Calcispongise of the second of these criteria. The well-marked keel of some specimens of B. carinatus seems, then, to be the combined result of variability and of littoral existence ; in other words, the species carinatus is not a good one, its sole character, the keel, not being a constant attribute of its organization, but a point which has been seized upon by a descriptive naturalist unacquainted from lack of material with both its history and its variations. It now remains to settle which of the numerous names given to this species should be adopted. In commencing the systematic study of the Echini I hoped to find in the synonymy of Agassiz sufficient evidence of care to enable future workers " to simplify their work by getting rid, to a great extent at least, of the bete noire of zoologists, and apply their time to better things." For the British naturalist, unfortunately, Prof. Agassiz's method of nomenclature prevents this desirable result; nor does he, in his reference to pre-Linnsean authors, preserve his consistency: his ' Chronological List,' for example, ascribes the name Brissus to Aristotle, but his synonymy to Klein (1734), while Echinus falls to the Greek naturalist and to Rondeletius (1554). This difficulty might, however, be pretty easily eliminated; but the omission of synonyms is a more serious matter in a work of such pretensions: thus, in the synonymy of B. unicolor we find a reference to B. ova-tus, Gmelin (1788), but no reference to the preceding species in Gmelin's list, which is B. unicolor itself, as is quite distinctly shown by the reference of both Gmelin and Agassiz to pi. xxvi. of Klein's \ Dispositio Echinodermatum.' The date of the specific term unicolor being then 1788, what is the date of carinatus 1 Agassiz, in his synonymy, ascribes it to Lamarck, and so places it in 1816 ; but a second reference to Gmelin shows that he recognized this species, his typographical error of 43 for 48 being corrected by bis own reference to p. 249 of Klein's (or rather Leske's) work, where the variety is spoken of as late-carinatus. I propose, therefore, to retain the name unicolor. Passing from the question of the identity of the species B. unicolor and B. carinatus, I come to the consideration of the forms Meoma and Metalia, which are reckoned as subgenera of Brissus by Prof. Alex. Agassiz. Under Meoma two species are included, one of which is found on either side the Isthmus of Panama-M. grandis and M. ventricosa. Whether a larger series than the Museum possesses at present will enable us to show the specific identity of these forms I do not know. The coarser and more distant tuberculation of M. grandis affords, as Agassiz has remarked, a ready mark of distinction ; and it seems, from a comparison of the arrangement of the |