74 COPEPODA 



am Ausseuaste der hinteren Antennen und einer eigentiimlichen Chitinlamelle am Rande der hinteren 

 Maxillipeden". The former character is found in G. tenuispinus as well (PI. Ill fig. 2 b), and the latter 

 is scarcely sufficient; the exopodite of the first pair of legs of M. maximus has 3 distinct segments, 

 each with a well developed outer seta, a character not found in any Gaidius or Gaetanus known to 

 me. If we regard the following species of Gaidius and Gaetanus as forming one group, the natural 

 division will probably be the following: i) the Gardius tenuispinus which has no frontal spine and 

 no lamina in the second basipodite of the maxillipeds; the second segment of the exopodite of the 

 antennae possesses a distinct process for the second seta, the first segment of the exopodite in the 

 second pair of legs has no glandular pore, and the inner margin of the second basipodite in the fourth 

 pair of legs in the young females has a few stiff setae, while in the young males it has a few 

 of usual structure, 2) the Gaidius brevispinus which has a well developed lamina in the maxillipeds 

 of the female, and the male of which has not a minute outer seta in the second segment of the 

 exopodite in the second pair of legs, 3) the Gaetanus Kruppi and latifrons, which differ from the two 

 preceding species by the frontal spine, and the presence of ten instead of eleven setae in the exopodite 

 of the maxillulae, but in other respects, except the lamina of the maxillipeds, agree with G. tenuispinus 

 4) Gaetanus minor which, except for the wanting glandular pore in the first outer segment in the second 

 foot, completely agrees with the preceeding group; and 5) Gaetanus pileatus and miles, which in ad- 

 dition to the wanting glandular pore of the second foot do not possess any process in the second 

 outer segment of the antennae, and have the inner margin of the second basipodite in the fourth foot 

 smooth in both sexes in the penultimate stage. For settling definitively the question of the relative 

 position of the species, the structure of the fifth foot in the male of G. miles must be known. At 

 present I am inclined to regard Gaidius tenuispinus and Gaetanus Kruppi as being more nearly related 

 to each other than the latter species is to Gaetanus miles. In addition to the mentioned characters all 

 the enumerated species have the lamina labialis rather simple, without the division in three portions 

 as in Euchirella, in contrast to Chiridius and Aetidius. The position of Chirudiua, to which not only 

 Ch. Streetsi but also pustulifera, abyssalis, notacantha, pannspina and spectabilis are referred, is a little 

 doubtful. These species are in several respects rather different, but show their affinity by the structure 

 of the oral surface of the labruin, and the structure of the fifth pair of legs in the male; the second 

 outer segment of the antennae have distinct setigerous processes, the outer surface of the maxillae 

 (PI. V figs. 5 c) is not very produced, the maxillipeds have a rather characteristic structure, the exo- 

 podite of the first foot is more or less distinctly three-divided, with three outer setae, and the glandular 

 pore of the first outer segment is wanting in the second foot; the inner margin of the second basi- 

 podite in the fourth pair of legs is either more or less smooth, or has a distinct corona of spines in 

 the mature female, but is completely smooth in both legs in the penultimate stages. Some of these 

 characters suggest affinity to Chiridius, others to Gaidius; if Wolfe n den's Mcsogaidius maximus 

 with a lamina in the maxillipeds, and the outer edged spines in the second pair of legs, really belongs 

 to this genus, a connecting link with Gaidius is found. The three last species ought perhaps, on ac- 

 count of the structure of the fifth pair of legs, to form an independent genus, and others, f. inst. Ch. pus- 

 tulifera, ought perhaps, as suggested by Sar s, to be referred to Undcnchcetc, the most nearly related genus. 

 As, however, the three or five species which I have referred to this genus form a well defined group, 



