Sd 
is highly chitinized, and when viewed from the dorsal aspect, is seen to contract gradually to 
a blunt point. There is a distinct crest, and a large horny rostrum with a moderately deep 
excavation and slightly divergent points. There are two distinct knobs in the hollow of the rostrum 
as shewn by Grrsprecut (PI. IV, fig. 4). The last thoracic segment is highly chitinized, and is 
produced posteriorly into strong spines. The spines extend beyond the end of the second seg- 
ment of the abdomen. The proportional lengths of the abdominal segments are distinctly different 
from those of the next two species. The combined length of the abdomen and furcal joints, is 
rather less than one-third of the length of the cephalothorax from the forehead to the base of 
the genital segment. The genital segment is about equal to the combined length of the next 
two segments. The second segment is about half the length of the genital segment. The third 
segment is about two-thirds the length of the second. The anal segment is as long as the second 
segment. The furcal joints are as long as the anal segment, and are about twice as long as broad. 
Length of female 2,1 mm. 
This species, when carefully looked for, will probably be found to have a moderately 
wide distribution in the warmer seas. | found examples of it on re-examining the plankton 
collected in the Gulf of Guinea by the ‘Buccaneer’ early in 1886, and also in the plankton 
collected by Professor HERpMaN during his traverse between England and Ceylon in 1902. 
2. <tideus armatus (Boeck). Plate IV, Figs. 14—25. 
Pseudocalanus armatus Boeck, 1872, p. 6. 
Etideus armatus Brady, 1883 (pars), p. 76. 
tideus armatus T. Scott, 1893 (pars), p. 70. 
itideus armatus Giesbrecht & Schmeil, 1898 (pars), p. 31. 
itideus armatus TY. Scott, 1901, p. 238. 
Aitideus armatus Wolfenden, 1902 (pars), p. 364. 
itideus armatus Sars, 1902, p. 25, pls. XIII & XIV. 
itideus tenuirostris Wolfenden, 1903, p. 266. 
Aitideus tenutrostris Wolfenden, 1904, p. 116. 
tideus armatus Cleve, 1904, p. 185. 
Eitideus armatus Sars, 1907 (a), p. 6. 
itideus armatus Farran, 1908, p. 28. 
itideus armatus van Breemen, 1908, p. 30, fig. 30. 
This. deus, although less common than the preceeding species, had apparently a 
slightly wider distribution in the area traversed by the ‘Siboga’, as shewn by the following records. 
Stat. $9, 8 specimen. — Stat. 118, 4 specimens. — Stat. 128, 3 specimens. — Stat. 141, 
6 specimens. — Stat. 143, 2 specimens. — Stat. 203 (1500 metres to surface), 8 speci- 
mens. — Stat. 276, 3 specimens. z 
This particular type from the ‘Siboga’ collections, appears to be identical with the form 
described by Borcx, which was very fully illustrated and described by Professor G. O. Sars in 
1902. It is quite distinct from the other two members of the genus described in this report. 
This species can be recognised by the following characters: — The forehead is not excep- 
tionally strengthened with chitin, and when viewed from the dorsal aspect, the front margin 
appears evenly rounded. There is no trace of a crest, although the forehead appears boldly 
37 
