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GIESBRECHT and ScumeiL doubtfully refer the two species described by Brapy in the 
‘Challenger Report’, as Hachaeta australis and Euchaeta pulchra, to Undeuchaeta major, but 
I regard them to be identical with the form described by Girsprecut as Uxdeuchaeta minor, 
and more correctly with Lussocx’s Undina plumosa. 
2. Undeuchaeta plumosa (Lubbock). Plate XXII, figs. 1—8. 
Undina plumosa Lubbock, 1856, p. 18, pl. IX, figs. 3—5. 
Euchaeta australis Brady, 1883, p. 65, pl. XXI, figs.. 5—11. 
Euchaeta pulchra Brady (pars) non Lubbock, 1883, p. 63, pl. XIV, figs. 6—g. 
Undeuchaeta minor Giesbrecht, 1888, p. 335. 
Undeuchaeta minor Giesbrecht, 1893, p 228, pls. 14 & 37. 
Euchaeta australs TY. Scott, 1893, p. 58,: pl. VI, fig. 23. 
Undeuchaeta minor Canu, 1896, p. 424. 
Undeuchaeta minor Giesbrecht & Schmeil, 1898, p. 34. 
Undina plumosa Giesbrecht & Schmeil, 1898, p. 52. 
Undeuchaeta minor Thompson & Scott, 1903, p. 243. 
Undeuchaeta minor Wolfenden, 1904, p. III. 
Undeuchaeta minor Cleve, 1904, p. 198. 
Undeuchaeta minor Farran, 1905, p. 35. 
Undeuchaeta minor Esterly, 1905, p. 149, fig. 17. 
Undeuchaeta australis Sars, 1905(a), p- 4. 
Undeuchaeta minor Pearson, 1906, p. 15. 
Undeuchaeta minor Sars, 1907 (a), p- 3. 
Undeuchaeta minor Farran, 1908, p. 37. 
Undeuchaeta minor van Breemen, 1908, p. 44, fig. 50. 
This species was well represented in the plankton collected by the ‘Siboga’, Thirty-nine 
females and eleven males were obtained at the following stations. 
Stat. 117°, I specimen. — Stat. 118 (HENSEN vertical net 900 metres to surface), 3 speci- 
mens. — Stat. 128 (HENSEN vertical net 700 metres to surface), 5 specimens. — Stat. 141 
(HENSEN vertical net 1500 metres to surface), 4 specimens. — Stat. 142, 2 specimens. — 
Stat. 143 (HENSEN vertical net 1000 metres to surface), 6 specimens. — Stat. 189", I speci- 
men. — Stat. 203 (HENSEN vertical net 1500 metres to surface), 4 specimens. — Stat. 216; 
I specimen. — Stat. 230 (HENSEN vertical net 2000 metres to surface), 7 specimens. — 
Stat. 243 (HENSEN vertical net 1000 metres to surface), 6 specimens. — Stat. 245, 4 speci- 
mens. — Stat. 276 (HENSEN vertical net 750 metres to surface), 5 specimens. 
The female of Undeuchaeta plumosa is distinguished from Undeuchaeta major, by the 
absence of any trace of a median crest on the forehead, and also by the absence of the hooked 
spine on the ventral surface of the genital segment of the female. 
I think there can be no doubt, after giving careful consideration to Lussocx’s description 
and figures, that the species described in the Transactions of the Zoological Society for 1856, 
as Undina plumosa, is identical with the male of Euchaeta australis Brady, and represents the 
missing male of Grrsprecut’s Undeuchaeta minor. LuppocK’s name plumosa ought, therefore, to 
be adopted as the specific name for this Usdeuchaeta instead of either australis or minor. 
The species described and figured in the ‘Challenger Report’ as the female of Auchaeta 
pulchra Lubbock, is really the female of Awchaela australis which I consider is identical with 
Undeuchaeta minor and to be the true female of Undeuchaeta (Undina) plumosa, GiESBRECHT 
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