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Show 1899.] CRUSTACEANS EROM LAKE TANGANYIKA. 709 is not excavated distally. It further agrees with the majority of the species of Caridina in the compressed and serrated rostrum, which, however, is much longer than in any species except C. gracilirostris de Man. It appears to differ frorn all except G. singhalensis Ortra. and C. brevirostris Stm. in the absence of a distinct antennal spine on the front of the carapace, and it certainly differs from all the species of Caridina, and I believe from all the other Atyidce, in the possession of a hepatic spine. The differences noted above in the shape of the first maxilla, the first maxilliped, and especially of the second maxilla, may possibly be of generic importance, as may also the fact that the dactylus of the last peraeopods does not differ markedly from those of the preceding pairs. The most striking and important character, however, is the reduction of the branchial system. This has not been examined (so far as I know) in Xiphocaris, but the closely-allied Troglocaris possesses eight gills (Claus), Atyaephyra, seven (Boas), Atya scabra and Caridina wyckii and typus, nine ; while there is no reason to anticipate any very great divergence in the closely-allied Atyoida or among the numerous species of Caridina which have not been examined in this respect. Further, all the forms hitherto examined possess (with a possible exception, as above noted, in the case of Atyoida) a complete series of epipods on the thoracic appendages. In the present form there are only four gills and no epipods at all. While there appears to be room for a further revision of the Atyidce based on a more complete examination of their morphology than that recently given by Ortmann, it seems plain that the form now described stands sufficiently far apart from the other members of the family to require the creation of a new genus for its reception. Family PALCEMONIDCE. PALCEMON MOOREI, sp. u. (Plate XL. figs. 20-24.) Description.-Eostrum (Pl. X L . fig. 20) horizontal, a little longer than the peduncle of the autennules and equal to or shorter than the antennal scale. The nearly straight upper edge bears 11-13 teeth, of which three are on the carapace, the fourth being just over or a little in frout of tbe posterior margin of the orbit. The distal tooth is close to the tip. The lower margin bears 3-4 teeth, the first being above the end of the first joint of the antennular peduncle. The usual antennal and hepatic spines are present on the carapace, the surface of which is elsewhere smooth. The third maxillipeds extend beyond the peduncle of the antennae by the length of their last joint. The first peraeopods (Pl. X L . fig. 21) extend to or a little beyond the tip of the antennal scales. The carpus is rather longer than the merus, and more than half as long again as the hand. The second peraeopod of a male specimen (Pl. X L . fig. 22) is about two-thirds the length of the body, and the distal end of the merus extends to beyond the middle of the antennal scale. The carpus P R O C . Z O O L . Soc.-1899, No. X L V I . 46 |