— 21 — 



Rhoda Sim (Boreophausia G. O. S.). 



This genus must be cancelled (see above), and its two 

 species are referred to the genus Thysanoëssa Brandt. 



Euphausia Dana. 



In the « Siboga » report I enumerated or described 21 

 valid species of this genus; furthermore all synonyms or 

 names to be cancelled were given. Here 6 new species are 

 added, so that the genus now comprises 27 species. In spite 

 of this great number adult males are always easy to deter- 

 mine, and in most cases adult females are far from diffi- 

 cult. The species may be referred to four groups, the first 

 and the fourth of which are well separated from the 

 others, while the second and the third, separated exclusely 

 by the existence or non-existence of a dorsal process on 

 third abdominal segment, are somewhat badly defined, 

 because two species show individual or local variation as 

 to the existence of this process. Nevertheless, I think it 

 useful for practical reasons to establish the two last-named 

 groups, as the exceptions are rarely met with and easily 

 pointed out. 



Group a. Species with two pairs of lateral denticles 

 on the carapace. No dorsal process on third to 

 fifth abdominal segment. 



Five species are known, viz. E. Krohnii Brandt, 

 E. diomedeœ Ortm., E. mutica H. J. H., E. recurva H. 

 J. H. and E. brevis H. J. H. E. diomedeœ Ortm. and 

 E. mutica H.J. H. have been described and figured in the 

 « Siboga » report ; of the three other species preliminary 

 descriptions are found in No. 42 of this Bulletin (E . 

 Krohnii Brandt is an older name for E. Millleri Glaus, 



(210) 



