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bifurcate base. The antennules are composed of twenty-three joints. The antennae, mandibles, 

 maxillae and maxillipedes are similar in structure to those of the genus Scokcithricella. The four 

 pairs of swimming feet are also similar to those of that genus. The fifth pair is very small. 

 Each foot is composed of a single joint attached to a basal part. 



Male. In general appearance it resembles the female. The frontal lens-like organ is 

 present. The rostral filaments are much longer and the basal part may possess a small secondary 

 apical spine. The antennules are composed of twenty joints. The antennae, mandibles, maxillae 

 and maxillipedes are similar to those of the female and are not modified. The four pairs of 

 swimming feet are also similar to those of the female, but the surface of the joints is less 

 spinulose. The fifth pair is well developed and prehensile. The basiopodite is two-jointed. The 

 exopodites of both feet are composed of two joints. The first joint of the right exopodite has 

 the basal part more or less produced internally. The second joint is forked. The apex of the 

 second joint of the left exopodite is furnished with a spine, and a tuft of hairs. The endopodite 

 is present on each foot, and is composed of a single joint. 



The form described by Giesbrecht in 1896 as Scolecithrix chelipes, undoubtedly belongs 

 to this genus. I have compared specimens of it that were found in plankton samples taken by 

 Professor Herdman in the Red Sea, during his traverse to Ceylon in 1903. The male fifth pair 

 of these specimens is identical with Giesbrecht's figure, and the forehead possesses the frontal 

 lens-like organ referred to above. 



The peculiar lens-like organ on the forehead of both sexes, along with the structure of 

 the male fifth pair of feet, readily separates this genus from any of the other members of the family. 



One species belonging to this new genus was found in the plankton collected by the 

 'Siboga'. Both male and female were obtained. The species is distinct from Giesbrecht's 

 Macatidrezuella {Scolecithrix) cliclipcs. 



1. Macandrezuella joanae nov. sp. Plate VI, figs. 12 — 23 (female). Plate XXIII, figs. 



9—15 (male). 



Female — length 3,6 mm. 



Seen from above, the body is oval and robust. The head is considerably contracted in 

 front, and the last thoracic segment is quite asymmetrical. Each side of the thoracic segment 

 is produced, and terminates in a curved spine. The spine of the left side is longer than the 

 one on the right side (Plate VI, fig. 12). Viewed from the side, the forehead appears rounded 

 and possesses a distinct lens-like organ, situated just behind the base of the rostrum. In end 

 view the organ is circular and chitinised (Plate VI, fig. 16). The left side of the last thoracic 

 segment is boldly but narrowly rounded, and is produced into a terminal curved spine, which 

 extends beyond the middle of the genital segment. The upper basal part of the spine forms 

 a distinct indentation with the dorsal margin (Plate VI, fig. 14). The right side of the last 

 thoracic segment is also boldly rounded, but the curved spine only reaches to the middle of the 

 genital segment. The basal part of the spine forms a distinct tooth with the dorsal margin of 

 the segment (Plate VI, fig. 15). The rostrum has a stout bifurcate base, and each ramus has 

 a filament articulated to it. 



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