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difference appears to be worthy of more than generic rank. Ozthona ought, I think, to be 
separated from the Cyclopidae and form the type of a distinct family. 
Three species of Ozthona were obtained from the plankton collected by the ‘Siboga’ 
in the Malay Archipelago. 
1. Ozthona rigida Giesbrecht. 
Oithona rigida Giesbrecht, 1896, p. 324, pl. 5, figs. IO—I5. 
Ozthona rigida Cleve, 1901, p. 45, pl. V, figs. 7—18. 
Oithona rigida Thompson & Scott, 1903, p. 255. 
Oithona rigida Cleve, 1903, p. 365. 
Oithona rigida Cleve, 1904, p. 193. 
Oithona rigida Wolfenden, 1905(a), p. 1023, pl. 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). 
Otthona rigida is closely related to Ozthona 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. 1 
2. Oithona plumifera Baird. 
Oithona plumifera Baird, 1843, p. 1093. 
Oithona plumifera Dana, 1852, p. 1100, pl. 76. 
Oithona plumifera 1. C. Thompson, 1888, p. 151. 
Oithona plumifera Giesbrecht, 1893, p. 537, pls. 4, 34 & 44. 
Oithona plumifera T. Scott, 1893, p. 89. 
Oithona plumifera Giesbrecht, 1895, p. 260. 
Oithona plumifera 1. 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. 
Orthona plumifera Williams, 1906, p. 651. 
Oithona plumifera Farran, 1908, p. 89. 
Oithona plumifera van Breemen, 1908, p. 167, fig. 183. 
This Ozthona 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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