Dr. 0. A. L. Morch on the Operculum and its Mantle. 117 1864, and many since made, have convinced me that, so far as regards the British flora, the raphidian diagnosis is not only quite true, but very natural. Yet, as formerly noticed, this character might more easily escape attention in Galiacese than in the other orders. Finally, the propriety of retaining Leea under Vitacese has been disputed; and the present observations will tend to support the conclusion of those botanists who, with Adrien de Jussieu and Lindley, persist that this genus ought not to be separated from Vitacese. Edenbridge, July 1/, 1865. [To be continued.] XIII. — On the Operculum and its Mantle (lobus operculigerus, pomatochlamys). By Dr. O. A. L. Morch. Ad ANSON* regarded the operculum of univalve shells as an-swering to the second valve of the bivalves — an opinion main-tained by Oken and lately by Dr. Grayt and Prof. MacdonaldJ. In this point of view the lobus operculigerus (Loven), or "the opercular mantle," would correspond with one moiety of the mantle of bivalves. Prof. Loven regards the bivalve shell as produced by a cloven or bipartite mantle, and the operculum as homologous with the byssus. Prof. Keferstein§ supports Loven's opinion, considering the slit in Emarginula and Tenagodus as a trace of division. The porous slit of Haliotis, Tenagodus, &c., corresponds with the notch or channel in canaliferous shells [Entostomata, Blv.). There is, however, a more important trace of division in many univalves — for instance, the dentated furrow in Monoceros, Pseudoliva, Ayicillaria, and some species of Mwre-r [Cerastes), but chiefly in Carinaria. In this last genus the keel is formed by the two sides of the shell, which are pressed against each other in such manner that a piece of paper can be introduced into the middle of the keel as far as the foetal shell. In Onustus (Humphr.) the two sides are cemented together, but the union can be clearly seen. Akera bullata shows something similar in * Hist. Naturelle du Senegal. t J. E. Gray " On the Operculum of Gasteropodous MoUusca, and an attempt to prove that it is homologous or identical with the second valve of Conchifera" (Annals and Mag. of Nat. Hist. ser. 2. v. p. 4/6; and Phil. Trans. 1833). X " On the Homologies of the so-called univalve shell and its Opercu-lum " (Proc. Linn. Soc. v. 1860). § Bronn u. Keferstein, Die Klassen u, Ordnungen des Thierreichs.
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