954 THE VOYAGE OF H.M.S. CHALLENGER. 



Lower Antennae with the peduncle elongate. 



First and Second Gnathopods alike in form, the wrist cup-like, the hand ovate, robust. 

 Uropods biramous ; in the first and second pairs the outer ramus generally shorter 

 than the inner. 



Telson elongate, more or less cleft, but sometimes to a very small depth. 

 The first pair of side-plates larger than the second. 



Genus Rhachotropis, S. I. Smith, 1883. 



1883. Rhachotropis, Smith, Proc. U.S. Nat. Mus., pp. 222, 229. 



1884. Tritropis, Schneider, Crust, og Pycn. Kvaenangsfjorden, p. 108. 



1887. „ Hansen, Oversigt over de paa Dijmphna-Togtet inds. Krebsdyr. 



S. I. Smith in 1883 substituted the name Rhachotropis for Boeck's Tritropis, that 

 being preoccupied, but gave no fresh definition of the genus. Carus in 1885 makes 

 Tritropis, Boeck, a synonym of " AmpMtonotus, Costa," but of the three species he 

 places under the genus so named one belongs to Dexamine, a second to Atylus, and the 

 third is undescribed. For what may be regarded as the original definition of Rhacho- 

 tropis, see Note on Boeck, 1870 (p. 400), genus Tritropis. 



RJiachotrojns aculeatus (Lepechin). 



1780. Oniscus aculeatus, Lepechin, Acta Petrop., p. 247, tab. 8, fig. 1. 



1824. Talitrus Edoardsii, Sabine, Appendix to Parry's Voyage of Discovery, p. 232, pi. ii. 



figs. 1-4. 



1826. ,, „ Ross, Appendix to Parry's Third Voyage, p. 119. 



1828. ,, ,, Ross, App. to Narr. of an attempt to reach the North Pole, No. 15. 



1835. Amphitlwe edvardsi, Owen, Appendix to the Narr. of a Second Voy. in search of a North- 

 west Passage, p. 90. 



1846. „ Edwardsii, Krayer, Naturh. Tidsskr., R. 2, Ed. ii. p. 76. 



1862. Ampliithonotus Edwardsii, Sp. Bate, Brit. Mus. Catal. Amph. Crust., p. 151, pi. xxviii. 



fig. 5. 



1865. „ aculeatus, Goes, Crust, amph. maris Spetsb., p. 10. 



1867. AmpMtonotus Edwardsii, Packard, Metn. Bost. Soc. Nat. Hist., vol. i. p. 297. 



1870. Tritropis aculeata, Boeck, Crust, amph. bor. et arct., p. 78. 



1870. ,, Helleri, Boeck, Crust, amph. bor. et arct., p. 79. 



1874. Ampliithonotus aculeatus, Buchholz, Die zweite Deutsche Nordpolarfahrt, ii. p. 316, 



Taf. iv. 



1876. Tritropis aculeata, Boeck, De Skand. og Arkt. Amph., p. 511. 



1876. ,, Helleri, Boeck, De Skand. og Arkt. Amph., p. 513. 



1883. Rhachotropis acideata, S. I. Smith, Proc. U.S. Nat. Mus., pp. 222, 229. 



According to Buchholz, who has given figures and a description, which clearly agree 

 with the Challenger specimens, the form which Boeck has named Tritropis helleri is only 

 the young of the older species, the absence of the carina from the earlier segments of the 





