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Show 528 MR. B. B. WOODWARD ON THE GROWTH AND [June 14, 7. On the Mode of Growth and the Structure of the Shell Velates conoideus, Lamk., and other Neritidce. By B. B. W O O D W A R D , F.G.S., F.R.M.S. (Communicated by Prof. FLOWER, C.B., President.) [Eeceived June 7, 1892.] (Plates XXXI. & XXXII.) At the June meeting of this Society in 1889 attention was drawn by the writer to the very peculiar method of growth of the shell which forms the principal subject of this communication, as was shown by sections of specimens then exhibited. Unfortunately a far too prevalent epidemic interfered for the time with further investigation, which on being resumed has lead to more extended inquiry than at first contemplated, with results, however, which it is hoped may prove to be of some interest. The species was then spoken of as Neritina schmideliana; but on reference to the literature it appears that this name cannot stand, since Chemnitz's description1 was published prior to the adoption, in the ' Conchylien-Cabinet,' of the binomial system of nomenclature. The next name in order of priority was that conferred by Gmelin in his edition of Linne's ' Systema Naturae'2, where he quotes Chemnitz, and under the impression it was a sinistral species calls it Nerita perversa. This, however, is such a complete misnomer that it seems wiser to set it aside, as recommended in such cases by the British Association Rules, and to adopt the specific name of conoideus conferred on it by Lamarck3. The generic name of Velates proposed byMontfort4 should also be adopted, since, judging from the evidence afforded by its shell, the animal must have differed in important respects from both of its nearest allies-Nerita and Neritina. Other conchologists have described and figured the shell, notably Deshayes, who also first figured the operculum ; but all save Schmidel5 seem to have confined their attention to its external aspect and to have overlooked its internal arrangement and its remarkable mode of growth after the earlier stages of its existence have passed. Before, however, this can be dealt with it is necessary, in the first instance, to briefly describe certain features in the internal structure of other members of the family to which it belongs. The Neritidse, it is well known, avail themselves largely of the molluscan faculty of removing portions of the shell that may be in the way of the animal in the course of its growth, and some of them in this manner convert the interior of their tenement into a single open chamber across which there projects from the side, immediately 1 Mart, and Cbemn. Conch.-Cab. ix. (1786) p. 130. 2 Linnaeus, Syst. Nat., ed. cura Gmelin (1789), torn. i. p. 3686. 3 Nerita conoidea, Ann. Mus. Paris, v. (1804) p. 93. 1 Conch. Syst. ii. (1810) pp. 354-6, fig. s A list of the more important references is given at the end of this paper. |