﻿_. COPEPODA 



am Aussenaste der hinteren Antennen imd einer eigentumlicheu Chitinlamelle am Rande der hinteren 

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

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

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

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

 division will probably be the following: i) the Gaiuiius tcnuispinus 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 j^air 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 Gaidiiis brcvispinus 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 s])ine, and the presence of ten instead of eleven setae in the exopodite 

 of the niaxillulae, but in other respects, except the lamina of the maxillipeds, agree with G. ieiiiiispimis 

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

 foot, completely agrees witli the preceeding group; and 5) Gaetanus pileatus and miles, whicli 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 

 jjresent I am inclined to regard Gaidius tcnuispifius anA Gactanus Kruppi ashQing^ more nearly related 

 to each other than the latter species is to Gactanus 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 Euchirclla, in contrast to Chiridius and Actidius. The position of Chirudina, to which not only 

 CIi. Strcctsi but also pitstulifcra, abyssalis, notacantha, parvispina and spectahilis are referred, is a little 

 doubtful. These .species are in several res])ects rather different, but show their affinity by the structure 

 of the oral surface of the labrum, and the structure of the fifth pair of legs in the nuile; the second 

 outer segment of the antennae have distinct setigerous i)rocesses, the oxiter 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 Wol fend en'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. iiist. Ch. pus- 

 tulifera, ought perhaps, as suggested by Sars, to be referred to Undenchcetc, the most nearly related genus. 

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



