65 



In the females, two of the six apical spines on the first maxilliped, in addition to being 

 furnished with rows of very short spinules, have also a number of moderately long and con- 

 spicuous spinules. The males of typical Euchaeta are easily separated from those of the next 

 genus, by the exopodite of both the right and left fifth foot terminating in a long spiniform joint. 



Seven species of typical Euchaeta were obtained from the plankton collected by the 

 'Siboga' in the Malay Archipelago. 



i. Euchaeta acuta Giesbrecht. Plate XX, figs. i — 9. 



Euchaeta acuta Giesbrecht, 1893, p. 246, pis. 16 & 37. 



Euchaeta acuta Giesbrecht & Schmeil, 1898, p. 38. 



Euchaeta acuta I. C. Thompson, 1903, p. 18. 



Euchaeta acuta Thompson & Scott, 1903, p. 244. 



Euchaeta acuta Wolfenden, 1904, p. 111. 



Euchaeta acuta Cleve, 1904, p. 190. 



Euchaeta acuta Sars, 1905 (a), p. 4. 



Euchaeta acuta Farran, 1905, p. 35. 



Euchaeta acuta Esterly, 1905, p. 157, fig. 23. 



Euchaeta acuta Pearson, 1906, p. 17. 



Euchaeta acuta Farran, 1908, p. 40. 



Euchaeta acuta van Breemen, 1908, p. 51, fig. 56. 



This species appeared to be very rare in the area traversed by the l Siboga'. Only one 

 female and three males were obtained. The specimens were found in the plankton collected with 

 the Hensen vertical net at the following stations. 



Stat. 141 (1500 metres to surface). — Stat. 148 (1000 metres to surface). — Stat. 185 (1536 

 metres to surface). — Stat. 203 (1500 metres to surface). 



The female of Euchaeta acuta resembles Euchaeta media very closely, but it can be 

 distinguished from it by the peculiar shape of the genital segment, when viewed from above. 

 The proximal margin of the left side is produced into a blunt process, which is distinctly notched 

 on the anterior surface. The posterior margin of the last thoracic segment appears evenly rounded 

 when seen from above, and from the side. The outer-edge spine on the second joint of the 

 exopodite of the second pair of feet, scarcely extends to the base of the first outer-edge spine 

 on the third joint. The second outer-edge spine on the third joint does not extend to the base 

 of the third outer-edge spine. The appendicular seta on the furcal joints is longer than the 

 others. Length, female 4,2 mm. 



According to the records, Euchaeta acuta has apparently a wide distribution in tropical 

 and temperate seas. 



2. Euchaeta concinna Dana. Plate XIX, figs. 21 — 27. 



Euchaeta concinna Dana, 1 849, p. 21. 



Euchaeta concinna Giesbrecht, 1893, p. 246, pis. 15, 16, 37. 



Euchaeta concinna Giesbrecht & Schmeil, 1898, p. 39. 



Euchaeta concinna. Cleve, 1901, p. 7. 



Euchaeta concinna Thompson & Scott, 1903, p. 244. 



Euchaeta concinna Cleve, 1903, p. 363. 



Euchaeta concinna Wolfenden, 1905 (a), p. 1008, pi. C, fig. 1 — 6. 



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SIBOGA-EXPEDITIE XXIX (7. Q 



