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difference appears to be worthy of more than generic rank. Oithona ought, I think, to be 

 separated from the Cyclopidae and form the type of a distinct family. 



Three species of Oithona were obtained from the plankton collected by the 'Siboga' 

 in the Malay Archipelago. 



i. Oithona rigida Giesbrecht. 



Oitliona rigida Giesbrecht, 1896, p. 324, pi. 5, figs. 10 — 15. 



Oithona rigida Cleve, 1901, p. 45, pi. V, figs. 7 — 18. 



Oithona rigida Thompson & Scott, 1903, p. 255. 



Oitliona rigida Cleve, 1903, p. 365. 



Oithona rigida Cleve, 1904, p. 193. 



Oitliona rigida Wolfenden, 1905 (a), p. 1023, pi. XCIX, fig. 42. 



This characteristic form appeared to have a moderately wide distribution in the area 

 investigated by the 'Siboga'. It was present in the plankton collected at the following stations. 



Stat. 47''. -- Stat. 50. -- Stat. 71. -- Stat. 142. — Stat. 165. -- Stat. 168. — Stat. 174. — 

 Stat. 205. — Stat. 213, 27 specimens. — Stat. 230 (HENSEN vertical net, 2000 metres to 

 surface). 



Oithona rigida is closely related to Oithona nana Giesbrecht, but it can readily be 

 distinguished by the structure of the fifth pair of feet of the female, and also by the difference 

 in the proportional length of the abdominal segments. 



This species has been recorded from the Red Sea, from the Indian Ocean, and from 

 off the coast of South Africa. 



2. Oitliona pliunifcra Baird. 



Oithona plumifera Baird, 1843, p. 193. 



Oithona plumifera Dana, 1852, p. 1 100, pi. /6. 



Oithona plumifera I. C. Thompson, 18S8, p. 151. 



Oithona plumifera Giesbrecht, 1893, p. 537, pis. 4, 34 & 44. 



Oithona plumifera T. Scott, 1893, p. 89. 



Oithona plumifera Giesbrecht, 1895, p. 260. 



Oithona plumifera I. C. Thompson, 1900, p. 284. 



Oithona plumifera Wheeler, 1900, p. 186, fig. 22. 



Oithona plumifera Cleve, 1901, p. 8. 



Oithona plumifera A. Scott, 1902, p. 408. 



Oithona plumifera Thompson & Scott, 1903, p. 255. 



Oithona plumifera Cleve, 1903, p. 365. 



Oithona plumifera Cleve, 1904, p. 193. 



Oithona plumifera Wolfenden, 1905 (a), p. 1023. 



Oithona plumifera Farran, 1905, p. 46. 



Oithona plumifera Esterly, 1905, p. 207, fig. 50. 



Oithona plumifera Norman & T. Scott, 1906, p. 185. 



Oithona plumifera Pearson, 1906, p. 32. 



Oithona plumifera Williams, 1906, p. 651. 



Oithona plumifera Farran, 1908, p. 89. 



Oithona plumifera van Breemen, 1908, p. 167, fig. 183. 



This Oithona proved to be moderately common. It was widely distributed throughout 

 the area investigated by the 'Siboga', as shewn by the following records. 



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