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Show 1899.] CRUSTACEAN FROM LAKE TANGANYIKA. 701 proportion, have larger spine-bearing antero-lateral margins, and are considerably more flattened. The front, too, though deflexed1, is less so than in Thelphusa. On the other hand, however, in several of the described species the abdomen of the male is of the so-called " hour-glass " shape 2, while in all one spine only seems to be developed on the carpal joints of the chelipeds, and the second antennal joint is distorted in the common manner. The condition of the chelipeds is, however, in some species of Thelphusa strictly comparable with that of Limnothelphusa, so that in. this respect we may consider the new form as occupying a somewhat intermediate position between these two old-established genera. T w o other little-known genera, however, Hydrothelphusa and Platythelphusa, must also, I suppose, be included in the group, though they are not mentioned by Ortmann. Of these, the former, from the streams of Madagascar, was first described in 18723 by A. Milne-Edwards. The description, however, wTas very brief, and though he has since 4 given a further account, as well as a figure of the dorsal aspect, our information is still unfortunately very incomplete. The front here, instead of being deflexed, is said to be almost horizontal, wdiile the carapace is considerably flattened and nearly quadrilateral. Only a single tooth, however, is present on the antero-lateral margin, in addition to that at the outer angle of the orbit. With this the description of Platy-thelphusa4, which actually comes from Lake Tanganyika, agrees in the main, but the antero-lateral margins are, in contradistinction, multi-dentate. Several figures of this form are given, but they are not, unfortunately, all one could wish. The figure of the antenna7; suggests that we are dealing with a simple undistorted condition of the joints, such as I have seen nowhere else but in Limnothelphusa, but the right and left antennas do not even agree one with another, according to the drawing. The fourth pair of walking-legs presents a peculiarity in being rather short, while the terminal joints are somewhat flattened and expanded, presumably for swimming purposes. The male of this form is unknown, so that it is to be hoped that Mr. Moore, during his present expedition to Tanganyika, will obtain further material, and so aid in clearing up this unsatisfactory state of our knowledge. Of the mode of life of either of these forms little or nothing can be learnt from the paper, which fact renders it still more difficult 1 Milne-Edwards's description of the genus Parathelphusa (see Ann. Sci. Nat. iii., Zool. t. 20) is exceedingly brief, and as regards the deflection of the front certainly misleading. Using this definition, one might readily conclude that Limnothelphusa comes under it, though an actual comparison shows that the resemblance is by no means exact. 2 Would it not be more satisfactory to keep these forms separate by constituting two new genera or sub-genera, this extremely prominent difference in shape of the male abdomen being made the basis of separation, as indeed has been done by Wood-Mason in his note on the genus (see Ann. & Mag. Nat. Hist. 1876, p. 122) ? 3 Ann. Sci. Nat. v., Zool. t. 15. * Ann. Sci. Nat. vii., Zool. t. 4. |