COPEPODA FROM IFALUK ATOLL 9 



1927, all of which show a certain relationship with Pseudocy clops, 

 have been united by M. S. Wilson (1958, p. 140) in the genus 

 Ridgewayia and placed in the separate family Ridgewayiidae. 



The generic characters of Pseudocyclops can be summarized as 

 follows : 



Females. — Body short and compactly built; cephalothorax in dor- 

 sal aspect ovoid, in lateral aspect with broadly rounded, almost 

 tumified head. Head and 1st thoracic somite usually separate, fused 

 in some species, produced anteriorly into downwardly dhected, strong, 

 1-pointed rostrum. Thoracic somites 4 and 5 separate or fused; 

 5th somite usually small; it may be produced into rounded lappet. 

 Abdomen composed of 4 somites; genital somite, resulting from 

 fusion of somites 1 and 2, with widely separated genital apertures. 

 Anal somite notably small, almost fused with furcal rami, usually 

 telescoped into 4th abdominal somite. 



Antennule short, scarcely reaching end of head or slightly longer, 

 18-segmented; segmentation may be fiu-ther reduced to 17 by almost 

 complete fusion of first two free segments, or to 14 by fusion of more 

 segments. Antennules strongly setose, part of the setae may be 

 plumose; aethetascs on basal and apical segments. 



Antenna with 3- or 4-segmented exopodite; segment 1 and apical 

 segment big; latter at right angle with rest of exopodite. Apical 

 part of 2nd segment of 2-segmented endopodite may be split off as 

 separate segment. 



Mandible with distinct line of fusion between coxa and basis; 

 this part of appendage lengthened. Exopodite 3- to 4-segmented, 

 distinct; endopodite 2-segmented. 



Maxillule with distinct praecoxal arthrite; endites of coxa and 

 basis small, almost hidden between arthiite and greatly produced 4 th 

 segment. Endopodite well developed, unsegmented ; exopodite present, 

 bearing at least 8 setae. Coxal epipodite present, bearing several 

 setae; basal exite absent. 



Maxilla short, compact, with 2 praecoxal endites, 2 coxal endites 

 and slightly bigger basal endite. Endopodite small, 2-segmented, 

 bearing some setae. 



Maxilhpede also short and compact; coxa with 3 lobes, basis short, 

 with terminal endite; endopodite likewise short, 4-segmented. 



Legs 1-4 with 3-segmented endopodites and exopodites. At fu'st 

 glance the setation and spinulation of the various species, as recorded 

 in the literatm-e, appears to be shghtly variable, but if we accomit 

 for a tendency of reduction of the external marginal spines of the 

 3rd exopodal segment of leg 1, a displacement of the terminal external 

 marginal spine to the apex in the 3rd exopodal segment of legs 1-4, 

 and a displacement of the apical internal seta, accompanying the 



