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female. There is practically no modification in their structure. The four pairs of swimming feet 

 are also similar to those of the female. The fifth pair is large and prehensile. The basiopodite 

 is composed of two joints. The exopodite of the right foot is usually very short and may be 

 one two, or three-jointed. The endopodite may be quite small, or of moderate length, but it 

 is alvvays present, and is composed of a single joint. The second joint of the basiopodite of 

 the right foot has frequently an articulated appearance in the swollen region, but this is pro- 

 bably due to defects in the mounted preparation. The two joints of the basiopodite of the left 

 foot are slender and cylindrical. The exopodite is two-jointed. The apex of the second joint 

 is usually furnished with two spines and a pad of hairs. The endopodite is small and one-jointed. 

 It does not exceed the length of the exopodite. The males appear to be slightly larger than 

 the females, but this, no doubt, is due to the longer abdomen. 



Seven species, four of which appear to be undescribed, were obtained from the plankton 

 collected by the 'Siboga' during the investigations in the Malay Archipelago. 



i. Scottocalanus securifrons (T. Scott). Plate XXV, figs. i — 9 (female). Plate XXVIII, 



figs. 1 — 9 (male). 



Scolecitlirix securifrons T. Scott, 1893 (pars), p. 47, pis. IV & V. 



Scolecithrix securifrons Canu, 1896, p. 425. 



Scolecitlirix securifrons Giesbrecht & Schmeil, 1898, p. 49 



Scolecithrix securifrons I. C. Thompson, 1903, p. 20. 



Scolecitlirix securifrons Cleve, 1904, p. 197. 



Lophothrix securifrons Wolfenden, 1904, p. 120, pi. IX. 



Scottocalanus acutus Sars, 1905 (b), p. 7. 



Scottocalanus securifrons Pearson, 1906, p. 19. 



Scottocalanus securifrons Farran, 1908, p. 57. 



Scolecithrix securifrons van Breemen, 1908, p. 76, fig. 88. 



Ten females and four males belonging to this species were obtained from the plankton 

 collected at the following stations. 



Stat. 118 (HENSEN vertical net 900 metres to surface), 1 specimen. — Stat. 128 (Hensen 

 vertical net 700 metres to surface), 1 specimen. — Stat. 141 (HENSEX vertical net 1500 

 metres to surface), 1 specimen. — Stat. 143 (HENSEN vertical net 1000 metres to surface), 

 1 specimen. — Stat. 148 (HENSEN vertical net 1000 metres to surface), 2 specimens. — 

 Stat. 184, 1 specimen. — Stat. 185 (HENSEN vertical net 1536 metres to surface), 1 speci- 

 men. — Stat. 203 (HENSEN vertical net 1500 metres to surface), 2 specimens. ■ — Stat. 216, 

 1 specimen. — Stat. 243 (HENSEN vertical net 1000 metres to surface), 1 specimen. — 

 Stat. 276 (HENSEN vertical net 750 metres to surface), 1 specimen. 



The females of this species are easily recognised by the produced, outwardly curved, 

 and pointed terminations of the last thoracic segment. The abdomen is very short. The com- 

 bined length of the abdomen and furca is contained three and a half times in the total length 

 of the ccp/ialol/iorax, from the apex of the crest to the base of the genital segment. The genital 

 tient is considerably swollen at the distal end, and its length is nearly equal to the combined 

 length of the next three segments. The ventral surface of the segment is much swollen, and 

 is produced posteriorly into a process, which partly overlapps the second segment. The posterior 

 rgin of the segment is fringed with fine spines. The rostrum is short and stout, and the apical 



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