n6 



10. Family Pseudodiaptomidae. 

 Genus Pseudodiaptomus Herrick, 1884. 



The members of this genus, established by Herrick in 1884, are readily recognised by 

 the structure of the fifth pair of feet of the two sexes. The fifth pair of the female consists 

 of a two-jointed basiopodite and an exopodite composed of two or three joints. The endopodite 

 is • stated to be entirely absent, but one of the species found in the plankton collected by the 

 'Siboga', shews an indication of what appears to be a very rudimentary endopodite. The male 

 fifth pair forms a prehensile appendage. The basiopodite is two-jointed. The exopodite of the 

 right side is composed of two or three joints. The last joint is usually claw-like. The exopodite 

 of the left side consists usually of two joints. The last joint is frequently lamelliform. 



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



1. Pseudodiaptomus aurivillii Cleve. 



Pseudodiaptomus aurivillii Cleve, 1901, p. 48, pis. VI & VII. 



Pseudodiaptomus aurivillii Thompson & Scott, 1903, p. 248, pi. II, figs. 24 — 26. 



This species although very limited in its distribution, proved to be rather plentiful in 

 one of the gatherings. It was present at the following stations. 



Stat. 16, 4 specimens. — Stat. 71, ó specimens. — Stat. 133, 3 specimens. — Stat. 174, S 

 specimens. — Stat. 213, 96 specimens. 



Pseudodiaptomus aurivillii is easily separated from the other members of the genus, 

 by the characters of the fifth pair of feet of the two sexes. The second joint of the exopodite 

 of the female fifth pair is very small. It terminates in a moderately long spiniform claw. The 

 right foot only of the male is furnished with an endopodite. The second joint of the basiopodite, 

 and the first joint of the exopodite of the right foot have each a strong outer edge spine. 



Cleve obtained the type specimens from plankton collected in the Malay Archipelago. 

 It has also been recorded, and partly illustrated from specimens found in the collections taken 

 by Professor Herd.man, during his investigations on the pearl banks in the Gulf of Manaar, Ceylon. 



2. Pseudodiaptomus elcvei nov. sp. Plate XXXVII, figs. 1 — 8. 



Female — length 1,75 mm. 



Seen from above, the female bears a general resemblance to Pseudodiaptomus aurivillii. 

 The last thoracic segment is produced into strong spines. Two dorsal spines are also present 

 on the surface of the last thoracic segment, just in front of the junction with the abdomen. 

 Viewed from the side, the forehead appears evenly rounded. The last thoracic segment is 

 rather narrowly rounded at the posterior end, and the dorsal spines are quite visible (Plate 

 XXXVII, fig. 3). 



The abdomen is composed of four segments. The combined length of the abdomen and 

 furca is contained one and a half times in the total length of the cephalothorax, from the 



116 



