COPEPODA 73 



(Ch. abyssalis and pustulifera). Corresponding to the difference between the mature females and males 

 a difference is sometimes found between the two sexes in the penultimate stage; in Gaidius tenuispi- 

 nus and Euchirella rostrata f. inst. the young female has along the inner margin of the second basi- 

 podite in the fourth pair of legs a few lamellous setae, while the young male has a few of usual 

 structure; in most species of Euchirella and Chirudina the margin is smooth in both sexes in the 

 penultimate stage. 



The Actidius is a well characterized genus which, as far as can be concluded from the wanting 

 glandular pore in Re I pes II and the well developed marginal setae in the fourth pair of legs, is a 

 rather primitive form. The Chiridius, to which genus I refer not only Ch. obtusifrons without distinct 

 rostrum, but also Ch. armatus in similarity to Sars and in contrast to Vanhoffen and Wolfenden, 

 is among other features characterized by the wanting plate-shaped process of the second basipodite of 

 the maxillipeds, the well developed exopodite of the first pair of legs with 3 setae, and the slender 

 marginal setae of the fourth pair of legs; as Giesbrecht had originally established the genus for a 

 species without rostrum, Wolfenden and Vanhoffen have accepted the name Pseudoaetidius for 

 Ch.armaius; Sars has judged this single character as being of minor importance, and he is certainly 

 right, especially when it is taken into consideration that a rudimentary slightly bifurcate rostrum is really 

 found. On account of the great number of glandular pores in the three last pair of legs (PI. II figs. 

 3 5 a) I once thought that Wolfenden was right; but as Ch. modestus u. sp., which in other respects 

 was like Ch. armatus, has 3 glandular pores (including one in Re I), I definitively accepted Sars' 

 definition. Sars has established a new genus jEtidiopsis synonymous with Wolfe n dens Faeroella, 

 especially characterized by well developed fifth thoracic tergite; as a fairly well marked fifth somite 

 is found in most specimens of Ch. armalus, I do not think this genus is a good one. A. Scott's new 

 genus Gaidiopsis (1909 p. 52), characterized by a very robust rostrum, is probably nearly related to 

 Chiridius. 



The genera Bradyctcs Farr. and Undinopsis G. O. Sars (synonymous with Bradyidius Giesbr.) 

 are nearly related; Pscudoeuchazte Sars is according to Far ran related to these genera as well as to 

 Bryaxis Boeck, the position of which seems to be a little doubtful on account of the poorly developed 

 outer ramus of the antennae. The position of Sars' genus Chiridiclla is very doubtful. I have not 

 had the opportunity of examining any specimens of the last mentioned five genera. 



According to Giesbrecht (1892 p. 249) the genus Gaidius has "rostrum kurz einspitzig" 

 and "Aussenast des ersten Fusses zwei . . . tmd Innenast des i. und 2. Fusses eingliedrig" and the only 

 difference from Gactanus is found in the frontal spine and the two-segmented endopodite of the second 

 pair of legs of the latter genus. The character found in the segmentation of the endopodite 

 of the second pair of legs is not of much value, as this articulation is well developed in 

 most species of Gaetanus as well as in Gardius drcvispmus, slightly developed in Gaetanus miles and 

 Gardius taiuispinus, and completely wanting in Gaetanus minor. The presence or absence of the frontal 

 spine seems to me to furnish a good specific, but scarcely a generic, character; Sars seems to share 

 this opinion, as he has established a Gactanus inermis without any spine. Wolfenden has established 

 a new genus Mcsogaidius (1911 p. 223) for his M. intermedius, perhaps identical with G. brevispinus. and 

 his M. maximus, because they combine the wanting frontal spine with "das Vorhaudensein eines Zipfel 



The Ingolf-Expcdition. III. 4. JQ 



