25 
described from the Antarctic as MRhzucalanus grandis, was identical with Rhzncalanus gigas, 
and the rather incomplete figures given by Brapy, was the chief reason for separating the two 
forms. The figure of the entire animal given by Brapy, 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. Caiman kindly examined the type specimens of AAzucalanus gigas in the 
British Museum, and I quote the following remarks from one of his letters to me. ‘The bottles 
Jabelled Rhzxcalanus 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 Brapy 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 Girsprecut’s fig. 10 on plate 12 of the Naples Monograph that I did not think 
“t worth while. The only difference from Gutrsprecut’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. GrespREcHT & 
ScumerIL state in ‘Das Tierreich’, that the male is unknown. WHEELER (1900), and van BREEMEN 
(1908), also failed to notice, that the male had been obtained both by Tuompson 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 ‘Axtomostraca from the Gulf of Guinea’ (1893), my father partly 
described and figured the male, stating that the fifth feet are alike in both sexes. 
1. Mecynocera clause 1. C. Thompson. 
Mecynocera claust 1. C. Thompson, 1888, p. 150, pl. XI, figs. I—4. 
Leptocalanus filicornis Giesbrecht, 1888, p. 334. 
Mecynocera claust Giesbrecht, 1893, p. 160, pls. 5, II, 35. 
Mecynocera claust T. Scott, 1893, p. 80, pls. 1 & 2 
Mecynocera clausi Giesbrecht & Schmeil, 1898, p. 23. 
Mecynocera claust Wheeler, 1900, p. 168, fig. 5. 
Mecynocera clause I. C. Thompson, 1903, p. 16. 
Mecynocera claust Thompson & Scott, 1903, p. 242. 
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SIBOGA-EXPEDITIE XXIXa@. 4 
