82 



spines on the apical lobes are more slender and flexible. The internal and external margins of 

 the claw-like spines are fringed with fine hairs. The apex is furnished with three long plain 

 filaments and five short organs with inflated heads. (Plate XXXV, fig. 15). 



The second pair of maxillipedes is similar to that of XantJwcalanus. 



The exopodite of the first pair of feet is three-jointed, and the endopodite is one-jointed. 



The exopodite of the second pair of feet is three-jointed, and the endopodite is two-jointed. 

 The second joint of the endopodite is furnished with three transverse rows of strong spines. 



The exopodites and endopodites of the third and fourth pairs of feet are each three- 

 jointed. The second and third joints of the endopodite of the third pair of feet are each furnished 

 with two transverse rows of strong spines. The second and third joints of the endopodite of 

 the fourth pair of feet are furnished with fine spines as shewn (Plate XXXV, fig. 1 7). 



The fifth pair of feet is symmetrical, but obviously rudimentary. The basiopodite is two- 

 jointed. The exopodite is distinctly two-jointed. The first joint is furnished with one outer-edge 

 spine. The second joint is broadly triangular in outline. It bears one apical and three subapical 

 spines. (Plate XXXV, fig. 18). 



Occurrence. — One specimen was obtained from the plankton collected with the 

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



The specimen is apparently an immature male, and the fifth pair of feet is very similar 

 to the figure given by Farran (1905 pi. XI, fig. 10). Farran regards his species to be closely 

 related to Oöthrix bidcntata (= Neoscolecithrix koelileri Canu). The present species, however, 

 does not appear to belong to that genus, as the short sausage-shaped organs, on the apex of 

 the first maxilliped, which are so characteristic of that genus are absent. Farran's specimens 

 measured 3,35 mm. 



Genus Onchocalanus G. O. Sars, 1905 (a). 



This genus is closely related to Xanthocalanus, but the females are easily recognised 

 by the strongly bifurcate rostrum, and by the apical lobe of the first- pair of maxillipedes being 

 furnished with a very stout curved claw. The posterior surface of the joints of the swimming 

 feet is armed with numerous fine spines. The fifth pair of feet is small. 



Two of the knovvn species were represented in the plankton collected by the 'Siboga'. 



1. Onchocalanus cristatus (Wolfenden). Plate XXXIV, figs. 1 — 8. 



Xantliocalanus cristatus Wolfenden, 1904, p. 119, pi. IX, figs. 18 & 19. 



Onchocalanus trigoniceps Sars, 1905 (a), p. 20. 



Xantliocalanus cristatus Pearson, 1906, p. 20. 



Onchocalanus cristatus Sars, 1907 (a), p. 3. 



Onchocalanus cristatus Farran, 1908, p. 49. 



Xantliocalanus cristatus van Breemen, 1908, p. 62, fig. 70. 



One female belonging to this species was found in the plankton collected with the 

 1 1 ensen vertical net at each of the following two stations. 



Stat. 148 (1000 metres to surface). — Stat. 185 (1536 metres to surface). 



S2 



