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Show 1897.] MR. W. E. COLLINGE ON EUROPEAN SLUGS. 445 Hab. Co. Dublin, Ireland ; Berkshire, Lancashire, Oxford, and Middlesex, England. Anatomy of the Generative Organs.-The organs are generally larger than those in A. hortensls, Fer. There are two vestibules, the lower one being considerably larger than the upper. The lower portion of the sperm-duct forms a globose swelling, above this a wide tube gradually tapering as it approaches the vas deferens, which is sharply marked off from the sperm-duct. The vas deferens is rather longer than in A. hortensls. The free-oviduct is very distinct from that in any form of A. hortensls which I have seen, and quite unlike any species of the A. hortensls group, in having the lower portion of the free-oviduct much larger and more globose than the upper, which is a narrow' tube (PL X X X I . fig. 19). The retractor muscle is attached to the upper part of the lower division of the free-oviduct. The receptacular duct is short, expanding terminally into the spherical sac, the receptaculum seminis. The remaining parts of tbe generative organs are similar to those of A. hortensls, Fer. A comparison of figures 18 and 19 with those numbered 6 to 12 will illustrate the more striking differences. In fig. 6 we have the terminal ducts of the generative organs of a typical A. hortensls, and a variation (fig. 12) which is the nearest to A. cceruleus. Alcoholic specimens of A. hortensls, Fer., and A. cceruleus are very readily distinguished from one another, even more so than when alive, although the external features of A. cceruleus are much more distinctly marked than in any other member of this group. 6. Synopsis and Classification of the Genus. The genus Arion as now understood by malacologists was constituted by Ferussac (11) in 1819. Brard (1815) divided Linne's genus Llmax into two genera, retaining Linne's name for those species without a shell, and constituted the new genus Limacella for those species possessing a shell. Jousseaume (13) is the only malacologist I know of who has adopted this classification. Hartman (1821) used the name of Limacia for the genus. Moquin-Tandon in 1855 (17) divided the genus into the two following subgenera:- Lochea, where the shell-plate was absent and represented only by small, unequal, isolated granulations. Prolepis, where the shell-plate was present in the form of an aggregation of separate calcareous particles. In 1868 Mabille (15) constituted the genus Baudonia for two species of Portuguese slugs, B. tlmlda and B. montana, which were distinguished from Arion by being anteriorly enlarged and depressed, with au almost smooth mantle, the head well separated from the body, and the tentacles small. It is hardly necessary to say that such superficial differences are of very little value, and PROC. ZOOL. Soc-1897, No. XXX. 30 |