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This species appears to be widely distributed in all the oceans. It is evident from Farran's 

 remarks (1908), and its presence in the deep collection at Station 203, although absent at the 

 surface, that it occasionally descends to considerable depths. Brady in his 'Challenger' report, 

 pointed out the characters of Ca/anus gracilis, and was of the opinion that future research 

 would render necessary the formation of a new genus for this species. 



2. Megacalanus robustior (Giesbrecht). 



Calanus robustior Giesbrecht, 1888, p. 332. 



Calanus robustior Giesbrecht, 1893, p. 91, pis. 7 & 8. 



Calanus comptus T. Scott, 1893, p. 26, pis. V & VI. 



Calanus robustior Giesbrecht, 1895, p. 248. 



Calanus robustior Giesbrecht & Schmeil, 1898, p. iS. 



Calanus robustior Thompson & Scott, 1903, p. 242. 



Calanus robustior Sars, 1905 (a), p. 1. 



Calanus robustior Wolfenden, 1905 («), p. 996, pi. XCVI, figs. 1 — 6. 



Calanus robustior Esterly, 1905, p. 129, fig. 5. 



This species has a close resemblance to Megacalanus gracilis and without a careful 

 examination may be easily mistaken for it. The robust form of the animal and the very swollen 

 genital segment, help to separate it from Megacalatius gracilis. It was noted at the following 

 'Siboga' stations but appeared to be rather rare. 



Stat. ij. — Stat. 40. — Stat. 110. — Stat. 117*. — Stat. 128. — Stat. 141. — Stat. 185. — 

 Stat. 189». — Stat. 245. — Stat. 276. 



The form recorded by my father from the Gulf of Guinea (1893) as ? Calanus cotnptus 

 Dana, and which he was inclined to consider as only a variety of Calanus gracilis, has been 

 identified by Giesbrecht & Schmeil as Calanus robustior, a conclusion that appears to be 

 quite correct. 



Megacalanus robustior has been previously recorded from the Atlantic, Pacific, and 

 Indian Oceans. 



3. Megacalanus princeps Wolfenden. Plate I, figs. 12 — 18. 



Megacalanus princeps Wolfenden, 1904, p. 112, pi. IX, fig. 1. 



Macrocalanus longicornis Sars, 1905 (a), p. 7. 



Megacalanus bradyi Wolfenden, 1905, p. 1, figs. 1 — 6. 



Megacalanus longicornis Pearson, 1906, p. 6. 



Megacalanus longicornis Farran, 1908, p. 21. 



Megacalanus longicornis van Breemen, 1908, p. 13, fig. 9. 

 nee Calanus princeps Brady, 1883, p. 36, pi. IV, figs. 3 — 7. 

 nee Macrocalanus princeps Sars, 1905 (a), p. 7. 



nee Megacalanus princeps Wolfenden, 1905, p. 3, pi. I, figs. 7 — 9. 

 nee Megacalanus princeps Pearson, 1906, p. 6. 

 nee Batkycalanus maximus Wolfenden, 1906, p. 26, pi. VIII. 

 nee Megacalanus princeps Farran, 1908, p. 21. 

 nee Megacalanus princeps van Breemen, 1908, p. 13. 



This fine species was represented in the 'Siboga' material by five specimens, all females, 



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