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described from the Antarctic as Rkincalanus gra/idis, was identical with Rliincalanus gigas, 

 and the rather incomplete figures given by Brady, was the chief reason for separating the two 

 forms. The figure of the entire animal given by Brady, is evidently drawn from a male and 

 apart from its larger size, there is nothing to distinguish it from the males found in the 'Siboga' 

 plankton. Dr. W. T. Calman kindly examined the type specimens of Rliincalanus gigas in the 

 British Museum, and I quote the following remarks from one of his letters to me. 'The bottles 

 'labelled Rkincalanus gigas in the Challenger collection seem to my eye, to contain specimens 

 'of more than one species, but I chose one of the largest specimens from Stat. 156 as most 

 'likely to be what Brady meant. None of the specimens seem to exceed 8,5 mm. in length 

 'excluding the caudal setae. In this specimen both rami of the first pair of legs have only 

 'two joints. I had begun to make a camera sketch of the limb to send you but it is so 

 absolutely like Giesbrecht's fig. 10 on plate 12 of the Naples Monograph that I did not think 

 'it worth while. The only difference from Giesbrecht's figure which I can see is that the 

 'terminal setae of the exopodite are relatively a trifle longer'. 



The terminal spine on the female fifth pair, apparently varies a good deal in different 

 individuals of the same size. In some cases it is quite stout and terminates abruptly, in others, 

 it is rather slender and tapers gradually to a fine point. The largest female from the 'Siboga' 

 plankton measured 5 mm. in length, exclusive of the caudal setae. 



Genus Mecynocera I. C. Thompson, 1888. 



The only known member of this genus, is easily distinguished from the other genera 

 belonging to the family, by its very long antennules, and by the structure of the first and fifth 

 pairs of feet. The exopodite of the first pair is three-jointed. The endopodite is composed of 

 one joint only. The fifth pair of feet is rudimentary, and only the exopodites are present. The 

 exopodite consists of three joints, and is attached to a two-jointed basiopodite. The second joint 

 of the exopodite is furnished with one plumose seta, and the third joint with five. Giesbrecht & 

 Schmeil state in 'Das Tierreich', that the male is unknown. Wiieeler (1900), and van Breemen 

 (1908), also failed to notice, that the male had been obtained both by Thompson at Madeira, 

 and by my father in the Gulf of Guinea. The late I. C. Thompson in his original description, 

 says 'males and females were both plentiful, and taken by surface tow-net at all the. places 

 visited'. In the Report on 'Entomoslraca from the Gulf of Guinea' (1893), my father partly 

 described and figured the male, stating that the fifth feet are alike in both sexes. 



]. JMccyjwcera clausi I. C. Thompson. 



Mecynocera clausi I. C. Thompson, 1888, p. 150, pi. XI, figs. 1 — 4. 



Leptocalanus filicornis Giesbrecht, 1888, p. 334. 

 Mecynocera clausi Giesbrecht, 1893, p. 160, pis. 5, 11, 

 Mecynocera clausi T. Scott, 1893, p. 80, pis. 1 & 2. 

 Mecynocera clausi Giesbrecht & Schmeil, 1898, p. 23. 

 Mecynocera clausi Wheeler, 1900, p. 168, fig. 5. 

 Mecynocera clausi I. C. Thompson, 1903, p. 16. 

 Mecynocera clausi Thompson & Scott, 1903, p. 242. 



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SIBOGA-EXI'EDITIE XXIX 11. 



