58 THE VOYAGE OF H.M.S. CHALLENGER. 



The stout build, and — in the female — the very short abdomen of this species are almost 

 sufficient to distinguish it at a glance from any other. On closer examination the most 

 conspicuous character is the remarkably long eighth joint of the anterior antenna in both 

 sexes ; the joint is evidently formed by the coalescence of four into one, traces of this 

 composition being, in some cases, quite distinct. The peculiar club-shaped filaments of 

 the anterior foot-jaw may perhaps be olfactory organs ; they seem at any rate to resemble 

 appendages which have been so considered in other Crustacea, and from their situation it 

 seems most likely that they are in some way subsidiary to alimentation. 



The occurrence of a four-segmented abdomen in both sexes is a little remarkable, and 

 though Sir John Lubbock's observation agrees with my own in ascribing only four joints 

 to the male abdomen, I was at first suspicious of a mistake. On careful re-examination, 

 however, I have been unable to see more than four joints in either sex, but the fourth in 

 the female is often so smallas to be almost obsolete (see fig. 11). Sir John Lubbock describes 

 the tail setse as four in number, and in many cases I have not found more than that ; but in 

 others (and this I suppose to be the normal condition) there is a very slender fifth seta, 

 attached, I think, between the third and fourth. 



This species, though not perhaps so abundant as Undina darwinii or Undina 

 longipes, is often found associated with them, and in very considerable numbers. 



2. Scolecithrix minor, n. sp. (PL XVI. figs. 15-16, and PL XVIII. figs. 1-5). 



Length, 1-1 5th of an inch (1*6 mm.). Cephalothorax moderately stout, broadly 

 rounded in front, postero-ventral angle acute, dorsal rounded off. Anterior antenna in the 

 male nineteen-jointed, angulated at the tenth joint, eighth joint very long, in the female 

 twenty-three- jointed, the large basal joint showing a faint trace of another articulation. 

 The mouth-organs are almost exactly like those of Scolecithrix dance, but the maxilla 

 (PL XVIII. fig. 3) is entirely destitute of an inner branch, and the anterior foot-jaws 

 of the male (fig. 4) are much more sparingly setiferous. The feet of the fifth pair in 

 both sexes are unbranched, in the female (PL XVI. fig. 16) minute, cylindrical, three- 

 jointed, the last joint furcate at the apex ; in the male (fig. 15) the right foot is longer 

 than the left, the last joint slender and bayonet-shaped, the antepenultimate bearing a 

 rather long lateral adpressed process ; the left foot ends in a trifid (?) slender claw. 



Habitat. — Scolecithrix minor was found only in a surface-net gathering from lat. 

 46° 46' S., long. 45° 31' E. (Station 146). In this bottle, however, it occurred in consider- 

 able abundance. 



The comparatively small dimensions and apparently imperfect development of some 

 of the parts of this animal led me to suspect that it might perhaps be only an immature 

 form. But it can scarcely belong to Scolecithrix dance — the only known Copepod 

 which possesses similar mouth-organs — the fifth pair of male feet being distinctly different. 



