1900.] FfiOM 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. Thysanoessa, Ortmann, Decap. u. Schizop., Plankton-Exp. 

 p. 14. 



1896. Thysancessa, Caullery, Ann. Univ. Lyon, ' Caudan' Crust., 

 Schiz. et Decap. p. 367. 



This genus is distinguished from the other Euphausiidae 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 the ' Challenger ' Eeports 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. Fork. 

 no. 7, p. 26. 



1885. Thysanoessa macrura, Sars, ' Ckallenger ' Schizopoda, 

 Reports, 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 longicaudato, the two other species of the genus, both 

 of wkich 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 tbe branches of the uropods, the inner being here 

 considerably, instead of ouly slightly longer than the outer. Sars 

 gives as a further distinction : " First pair of ltgs [second maxilli- 

 peds] much smaller than in last species [gregaria], nieral [fourth] 

 joint scarcely reaching beyond middle of antennal scale." He 

 does not gi\e 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 



