1899.] CRUSTACEANS FltOM LAKE TANGATfYIKA. 709 



is not excavated distally. It further agrees with the majority of 

 the species of CaricUna in the compressed and serrated rostrum, 

 which, however, is much longer than in any species except 

 C. gracilirostris de Man. It appears to differ fi'om all except 

 C. singhalensis Ortm. and C. hrevirostris Stm. in the absence of a 

 distinct anteonal 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 geueric 

 importance, as may also the fact that the dactylus of the last peraeo- 

 pods does not differ markedly from those of the preceding pairs. 



The most striking and important character, however, is the 

 reduction of the branchial systeui. 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 scahra 

 and Caridina wychii 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. Turther, 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 

 Atyidoi 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 Pal^monid^. 



PALJiMON MOOREi, sp. \i. (Plate XL. figs. 20-24.) 



Description. — Eostrum (PI. XL. fig. 20) horizontal, a little 

 longer than the peduncle of the antennules 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 front of the 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 

 (PI. XL. 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 (PI. XL. 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 



Pkoc. Zool. Soc— 1899, No. XLYI. 46 



