33 



Clausocalanus furcatus Cleve, 1903, p. 360. 

 Clausocalanus furcatus Cleve, 1904, p. 188. 

 Clausocalanus furcatus Sars, 1905 (a), p. 3. 

 Clausocalanus furcatus Wolfenden, 1905 (a), p. 999. 



Clausocalanus furcatus appeared to be almost as widely distributed in the regiem 

 traversed by the 'Siboga', as the previous species. The following is the record of the stations 

 where it was noted. 



Stat. 16. - ■ Stat. 40. - - Stat. 81. - - Stat. 96 (day). - - Stat. 96 (night). — Stat. 98. — 

 Stat. 99. -- Stat. 110. — Stat. 112. — Stat. 118. -- Stat. 121. — Stat. 128. -- Stat. 138. — 

 Stat. 141. -- Stat. 142. -- Stat. 143. — Stat. 148. -- Stat. 168. — Stat.' 184. — Stat. 1S5. — 

 Stat. 203 (surface). - • Stat. 203 (1500 metres to surface). - - Stat. 204. — Stat. 205. — 

 Stat. 213. - Stat. 215'. -- Stat. 217 (horizontal cylinder). -- Stat. 220 (vertical net). — 

 Stat. 224. -- Stat. 230. — Stat. 271. -- Stat. 276. — Stat. 282. — Stat. 315. 



The females of this Clausocalanus, are distinguished from those of Clausocalanus arcui- 

 cornis, by the genital segment being shorter than either of the next two segments, and by the 

 furcal joints being twice as long as broad. 



This species has a similar distribution in the great oceans as the previous one. 



Genus Oxycalanus Farran, 1908. 



This genus was established by G. P. Farran in 1908, for the reception of a Calanoid 

 nearly related to Spinocalanus, but the possession of a strong bifurcate rostrum at once separates 

 it from that genus. 



A number of specimens of a form apparently belonging to this genus, were found in the 

 'Siboga' plankton. I was inclined at first, to regard them as identical with Farran's species, but 

 further consideration revealed some important differences, which appear worthy of specific rank. 



Only one species belonging to this genus was observed. 



1. Oxycalanus semispinus nov. sp. Plate II, figs. 9 — 21. 



Female — length 2,4 mm. 



The ccplialothorax is oblong ovate in dorsal view, and is slightly contracted in front. The 

 head is completely fused with the first thoracic segment. The fourth and fifth thoracic segments 

 are fused together. The lateral margins of the last segment are rounded, and slightly produced 

 posteriorly. The rostrum is well defined, and is produced into two sharp points (PI. II, fig. 1 1). 



The abdomen is four-jointed, and is equal to rather more than one-third of the length 

 of the ccplialothorax. The genital segment is asymmetrical. This is due to a slight protuberance 

 on the right side. It is equal to the combined length of the second and third segments. The 

 third segment is slightly shorter than the second. The anal segment is equal to two-thirds of 

 the length of the third segment. The furcal joints are slightly longer than broad, and are about 

 as long- as the anal segment. 



The antennules are twenty-four-jointed and reach to the anal segment. The terminal joint 

 is very small, and is furnished with one sensory filament. 



33 



SIBOGA-EXPED1TIE XXIX ö. _5 



