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Show 594 MR. G. A. BOULENGER ON THE [Nov. 17, To render my synopsis perfectly intelligible, it is, however, necessary to say a few words, by way of introduction, concerning the external structure of the Tadpole and the manner in which its characters are described. 1. The Form.-The head and body are so fused that it is extremely difficult to discern the limit between the two. The term body is therefore used as meaning both head and body. Its longitudinal measurement is taken to the origin of the hind limbs. The tail consists of a fleshy muscular portion bordered above and below by membranous expansions, termed respectively the upper and lower crest. By depth of the tail is meant its greatest depth, crests included, and the length is measured from the posterior extremity of the body. 2. The Mouth.-This term is used in its wider sense, i. e. to include the much-developed lip, surrounding, like a funnel directed downwards, the horny beak (fig. 1, m.), not unlike that of a cuttlefish, which forms the entrance to the mouth proper (b.o.). The characters offered by this circular lip are among the most important for the distinction of species, and have formed the subject of a valuable paper by Heron Royer and Van Bambeke (Arch, de Biol. ix. 1889), to which I have already referred and shall often have to refer again. This lip may be entirely bordered by fleshy papillce (I.p.), or these may be restricted to the sides or to the sides and the lower border. Its inner surface is furnished with ridges armed with series of minute, bristle-like, erect horny teeth (fig. I, t.), each of which, when strongly magnified, is seen to be formed of a column of superposed cones, hollowed out at the base and capping each other; the summit of each of these cones is expanded, spatulate, hooked backwards, and usually multicuspid. By drawing an imaginary line across between the mandibles, the lip may be divided into an upper and a lower portion, the series of teeth above the upper mandible being termed upper labial, those below the lower mandible being lower labial. These are described as 1st, 2nd, 3rd, & c , proceeding from the outer border towards the beak in both the upper and the lower lip, as shown in the accompanying figures. Each series is reckoned as one, whether continuous or more or less interrupted in the middle. This method of describing appears to me far more simple, and at the same time more correct, considering the great amount of individual variation, than that used by the authors named above, who distinguish between "median" and "lateral" series according as to whether or not the series is broken up in the middle. The first series, either in the upper or lower division of the lip, may be marginal (fig. 1, A, £.1), or it may be within the border, which is then occupied by fleshy papillae (fig. 1, B). I have expressed the arrangement of the series of teeth by formulas-• 3, for instance, indicating the number in the upper and lower divisions of the lip, the figures being separated by a transverse line corresponding to the position of the horny beak. The labial teeth are usually arranged in a single row on each ridge (fig. 1, A) ; in the |