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One specimen was obtained from the plankton collected at each of the following ten stations. 



Stat. 93. — Stat. 99. — Stat. 110. — Stat. 142. — Stat. 169. — Stat. 174. — Stat. 203 

 (HENSEN vertical net, 1500 metres to surface). — Stat. 225. — Stat. 229. — Stat. 315. 



Acartia spinicauda has been recorded from the Chinese Coast, the Arabian Sea, and 

 the Malay Archipelago. 



2 1 . Family Tortanidae. 

 Genus Tortanus Giesbrecht, 189S. 



The members of this genus are readily separated from the other Calanoids by the 

 peculiarly twisted form of the anal segment, and by the very large eye that gives the head, 

 when seen from the side, an appearance very similar to some of the Cladocera. 



Four species were found in the plankton collected by the 'Siboga'. Two of the species 

 appear to be undescribed. 



1. Tortanus barbatus (Brady). Plate LV, figs. 16 — 18. 



Corynura barbata Brady, 1883, p. 71, pi. XXXI, figs. 10 — 12. 



Corynura denticulata Giesbrecht, 1889, p. 26. 



Corynura denticulata Giesbrecht, 1893, p. 525, pis. 31 & 42. 



Corynura barbata, Giesbrecht, 1893, p. 525. 



Tortanus barbatus Giesbrecht & Schmeil, 1S9S, p. 158. 



Tortanus denticulatus Giesbrecht & Schmeil, 1898, p. 15S. 



Four females belonging to the above species were found in the plankton collected with 

 the Hensex vertical net at Station 185, 1536 metres to the surface. 



The abdomen is composed of three segments. The anal segment is long and narrow. 

 The fifth pair of feet consists of two free joints attached to a basal part. The second free joint 

 of the left foot is long and comparatively stout. The middle of the inner margin is furnished 

 with a tuft of five curved lamelliform teeth. The second free joint of the right foot is scarcely 

 equal to half the length of the second free joint of the left foot. The inner margin has 110 

 tuft of teeth (Plate LV, fig. 18). 



The difference between Tortatms barbatus and Tortanus denticulatus appears to be so 

 very slight that I am inclined to regard the two forms as identical. The tuft of teeth on the 

 second free joint of the left foot is more compact than in Tortanus denticulatus. That appears 

 to be the only difference, except that Tortanus denticulatus has 110 whip-like ends to the teeth 

 as shewn in Bradv's figure. The tuft of teeth in the 'Siboga' specimens is compact, but the 

 ends are not whip-like. 



I have specimens of Tortanus barbatus from plankton collected in Patani Bay, Siam, 

 with the whip-like ends of the teeth reaching to midway between the tuft and the distal end 

 of the joint. The whole of the teeth in these specimens have whip-like ends. The thin ends 



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