I. '08. 26 



II. Rostrum only reaching as far forward as 

 the basal articulation of the eyestalks ; a 

 post-ocular spine present, gastro-hepatic 

 groove well marked ; second and especially 

 third joint of antennnlar peduncle slender, 

 antennal scale very strongly narrowed 

 apically and more than three times as long 

 as broad ; fifth pereiopod less than half the 

 length of the carapace (excluding ros- 

 trum) ; outer uropod five to five and a half 



times as long as broad, . . S.arcticus Hp. 30). 



Young mastigopi of these two species, in which the eyes 

 are not w^hoUy black, are most easily distinguished from one 

 another by the stout or slender second and third joints of the 

 antennular peduncle ; some of the other characters mentioned 

 above are not valid for these young specimens. 



Sergestes robustus, Smith. 

 Plate III, Figs. 1-12. 



Sergestes rohu^tus, Smith, 1882, PI. xvi, figs, 5-8. 

 Sergestes rohustus, Smith, 1884, PI. viii, figs. 3-6. 

 Sergestes rohustus, Smith, 1886, PI. xx, fig. 6. 

 Sergia rohusta, Ortmann, 1893. 

 Sergestes rohustus, Hansen, 1896. 

 Sergestes rohustus, Hansen, 1903 (2), figs. 6 and 7. 

 Sergestes inerinis, Hansen, 1903 (2), figs. 1-5. 

 Sergestes rohustus, Hansen, 1908. 



The carapace is laterally compressed and is about half the 

 length of the abdomen, excluding the telson. It is evenly 

 rounded dorsally, and is produced anteriorly to a strongly 

 laterally compressed rostrum , w^hich reaches as far forw-ard as 

 the middle of the corneal portion of the eye. The rostrum 

 (fig. 2) is usually provided wdth two obscure denticles on its 

 dorsal aspect near the apex ; the inferior margin is slightly 

 convex and is furnished basally with a fringe of plumose setae. 

 The gastro-hepatic and cardiac grooves of the carapace are 

 almost obsolete ; dorsally no trace of either is visible. The 

 branchial region is defined superiorly by a well-marked groove. 

 The position of the hepatic spine is occupied by a slightly 

 elevated but obscure lobe ; there is no post-ocular spine. 



The third and fourth ahdominal somites exhibit a shallow 

 dorsal depression, the others are evenly rounded above. The 

 sixth somite is rather more than one and a half times the 



1 In the lists of species caught during the Scotch International Plank- 

 ton Investigations Sergestes atlanticus and " Sergestes Colletti " appear 

 (see Pwb. Circ, 1909, No. 48, p. 135). Dr. T. Scott, who has kindly re- 

 plied to m\; queries on the subject, is now of the opinion that the speci- 

 mens referred to the former species are only young S. arcticiis, and he also 

 informs me that ''Sergestes Colletti '' is a misprint ior Siphonoecete^ 

 Colletti. 



