30 L. Agassiz on the Echinodermata. thin, pellucid, pale, with whitish rays and darker submarginal streaks; covered with a thin pale brown laminar periostracum; lunule and lozenge smooth, keeled; lateral teeth very thin. — Hab. China. Very like M, Helvacea, but smaller and much more com-pressed. V. — Prodromus of a Monograph of the Radiata and Echino-dermata, By Louis Agassiz, D.M.* Having had occasion for some years to examine a great number of Echinodermata, and having paid particular attention to their general organization, but more especially to the solid portions of their integument, which have been hitherto consi-dered the most important of their external characteristics, I have felt induced by these circumstances, and others no less favour-able to inquiries of this kind, to publish the following outline of a survey of the genera of this class as an introduction to a more general and critical work, in which I purpose hereafter to treat of all the species and their comparative anatomy. The section of radiated animals to which the Echinodermata belong, should, in order to be characterised in a general man-ner, be reduced to three classes : the Polypi, the Acalephae, and the Echinodermata. Intestinal worms, and a great part, if not the whole, of the Infusoria should be restored to the section of articulated animals. That I may not be compelled for a moment to lose sight of the main object of this paper, I think it advisable, as M. de Blainville has already proposed some of these changes, to refer for information as to the limitation of these classes to the article " Zoophytes" in the 'Dictionnaire des Sciences Naturelles/ though there are several points of detail on which he and I disagree. The class of the Echinodermata confined within its natural limits should contain no more than the three genera Holothu-ria, Echinus, and Asterias of Linnaeus, which have become the * Translated from the extract in the ' Annales des Sciences Naturelles,' Mai 1837, taken from the ' Memoires de la Societe des Sciences Naturelles de Neufchatel,' tome i.
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