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Show 1 900.] FROM THE FALKLAND ISLANDS. 547 1892. Thysanoessa, Norman, Ann. Mag. Nat. Hist. ser. 6, vol ix p. 462. 1893. Thysanoessa, Stebbing, Hist. Crust., Internat. Sci. Ser. vol. lxxiv. p. 264. 1893. 2'hysanoessa, Ortmann, Decap. u. Schizop., Plankton-Exp. p. 14. 1896. Thysanoessa, Caullery, Ann. Univ. Lyon, ' Caudan' Crust., Schiz. et Decap. p. 367. This genus is distinguished from the other EuphausiidaB by having the second maxillipeds greatly produced, with their two terminal joints carrying spiniform setae on both margins. In his preliminary notices of the 'Challenger' Schizopoda, Professor Sars speaks of the long second maxillipeds as the second pair of legs, but in tbe ' Challenger' Beports he calls them the first pair of legs- a vacillation which points to the ever-perplexing question whether an appendage ought to be named according to its undoubted homology or according to its actual structure, or according to some better but not yet invented method. It is, to say the least, very convenient to speak of three pairs of maxillipeds throughout the Malacostraca, with exception of the Isopoda and Amphipoda, in which the terms first and second gnathopods have won acceptance in place respectively of the second and third maxillipeds. THYSANOESSA MACRURA Sars. 1883. Thysanoessa macrura, Sars, Christiania Vidensk. Forh. no. 7, p. 26. 1885. Thysanoessa macrura, Sars, ' Challenger' Schizopoda, Beports, vol. xiii. p. 125, pi. 23. figs. 1-4. 1893. Thysanoessa macrura, Ortmann, Decap. u. Schizop., Plankton-Exp. p. 14. This species, in common with T. gregaria Sars, is distinguished by a tooth on the lateral margin of the carapace from Kroyer's neglecta and longicaudata, the two other species of the genus, both of which are devoid of such a tooth. Kroyer's species also have a simple preanal spine, whereas that spine in macrura has from two to three teeth, and in gregaria may have a pectination of thirteen, though Ortmann reports a specimen in which it has only two teeth, thus undermining the value of this specific character. The present species is distinguished from T. gregaria by the rostrum more broadly triangular and apically more acute, by the greater length of the sixth pleon-segment, and by the comparative length of the branches of the uropods, the inner being here considerably, instead of only slightly longer than the outer. Sars gives as a further distinction : " First pair of ltgs [second maxillipeds] much smaller than in last species [gregaria], moral [fourth] joint scarcely reaching beyond middle of anteunal scale." He does not give a detail-figure of these appendages, but in the lateral view of the animal the three terminal joints combined are much shorter than the fourth joint of the appendage in question, and |