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and Schmeil doubtfully rcfer the two species describèd by Bradv to Undeuchaeta major, but 

 I fail to see any reason for this. Neither Brady's descriptions or ligures indicate the presence 

 of a median crest on the forehead, or of a hooked spine on the ventral surface of the genital 

 segment. These two characters are quite obvious in the 'Siboga' specimens of the female of 

 Undeuchaeta major. It is extremely unlikely that Bradv would overlook the median crest, had 

 it been present in the 'Challenger' specimens. The hook at the genital opening might be broken, 

 as I have noticed it to be slightly damaged in some of the 'Siboga' specimens, but none had 

 the median crest damaged in any way. The dorso-lateral spine, on the right of the genital 

 segment when seen from above, is not always visible when the female is lying perfectly flat 

 on its left side, and it cannot be seen at all when lying perfectly flat on the right side. A slight 

 movement one way or the other, from the true lateral position is sufficiënt to bring the spine 

 into view. This would account for its absence in the figure on Plate XXI, and its presence 

 in the figure on Plate XIV. The view of the furcal joints in the latter figure shews quite well, 

 that the specimen was not lying perfectly flat. The absence of the median crest is of more 

 importance than the want of the spine. Female — length 3,5 — 4,5 mm. 



The fifth pair of feet of the males found in the 'Siboga' plankton is identical with the 

 figures given by Lubbock and by Bradv. The right and left sides have been reversed in the 

 figure in the 'Challenger Report'. 



The exopodite of the right and left foot is three-jointed. The endopodite of the right 

 foot is apparently two-jointed. The endopodite of the left foot is orily one-jointed. The second 

 joint of the left exopodite is furnished with a strong spine on its inner distal angle. The middle 

 of the inner margin of the third joint bears a tuft of setae. The apex of the joint is prolonged 

 into a spine. 



The exopodite of the first pair of feet is distinctly three-jointed, but there is no outer- 

 edge spine on the first joint. The endopodite of the second pair of feet is only one-jointed. 



The various mouth organs are much reduced as in the males of Euchaeta. ■ 



The last thoracic segment is very slightly produced and the extremities are rounded. 

 The rostrum is similar to the female but rather smaller. Male — length 3,2 — 3,6 mm. 



The species is widely distributed. I have examined males and females from collections 

 of plankton taken in the deep water of the Faröe Channel, by the Scottish International 

 Fisheries Cruiser 'Goldseeker'. There appears to be no difference between the Xorth Atlantic 

 type of Undeuchaeta plumosa, and those taken by the 'Siboga'. 



3. Undeuchaeta intermedia nov. sp. Plate XXIII, figs. 1 — 8. 



Female — length 4,5 mm. 



The cephalothorax is oblong ovate and moderately robust. The head is distinctly separated 

 from the first thoracic segment, and is furnished with a very faint median crest, which may 

 only be a slight thickening of the integument, and a moderately long, one-pointed rostrum. 

 The fourth and fifth thoracic segments are completely fused. The last thoracic segment is 

 slightly asymmetrical, and both sides are prolonged into fine points. 



The abdomen is composed of four segments. The combined length of the abdomen and 



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