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Show 1881.] LAKES TANGANYIKA AND NYASSA, ETC. 293 This is another instance of a species from Tanganyika having very much the appearance of a marine form. At present the operculum and animal are unknown; and therefore I place it provisionally in the genus Melania ; for it approaches in some respects certain aberrant forms of that group, e. g. M. brevis, d'Orbigny, and M. parva, Lea. The colour is not uniform in tint; for beneath the whitish infra-sutural line the brown is paler, then comes a darker zone gradually blending into a paler one. The body-whorl too has an ill-defined basal zone. 36. TIPHOBIA HOREI, Smith. (Plate XXXIV. fig. 28.) Tiphobia horei, Smith, Proc. Zool. Soc. 1880, p. 348, pi. 31. f. 6-66. When describing this very remarkable form, I was unable to give any account of the operculum. Fortunately, one of the specimens brought home by Mr. Thomson had that appendage adhering to the interior. It is almost black, horny, elongate-subovate, rather concave exteriorly, paucispiral in the centre, which portion is surrounded by apparently concentric layers. The lower side has a glossy border, which is broadest on the outer margin, narrow and slightly thickened on the inner or columellar edge. It is not sufficiently large to close the aperture of the shell as in the genus Paludina ; and the paucispiral character of the early stage of its growth confirms m y original opinion that the species should be classed with the Melaniidae. It is by no means a common shell according to the observation of Mr. Thomson, being restricted to a certain part of the lake, and even there not abundant. The absence of an epidermis i3 still maintained in the specimens now under examination ; and this very remarkable peculiarity may be considered eventually a sufficient distinction to separate the genus from the Melaniidae. 37. NEOTHAUMA TANGANYICENSE, Smith. Neothauma tanganyicense, Smith, Proc. Zool. Soc. 1880, p. 349, pi. 31. figs. 7-7c In this instance also I am enabled to give an account of the operculum. It is of a reddish colour, and normally paludinoid, the nucleus being situated about midway between the inner or columellar border and the centre. One of the specimens is unusually acutely carinate around the centre of the body-whorl, and very deep in the suture. 38. PALUDINA CAPILLATA, Frauenfeld. Paludina capillata, Frauenfeld, Proc. Zool. Soc. 1865, p. 659 ; 1877, p. 717, pi. 74. figs. 3-4. Hab. Lake Nyassa {Kirk); between it and the east coast {Thomson). |