COPEPODA FROM IFALUK ATOLL 55 



antennular segment 3 small and apparently free and partly visible 

 from above. Between the basal antennular parts there is a distinct, 

 bifid rostrum; the points curve outward and are strongly chitinized 

 (fig. 15d). There is the indication of a rudimentary maxillary hook: 

 the flattened edge of the cephalic somite shows a small tooth at the 

 level of the fusion between antennular segments 1 and 2 (fig. 15d). 

 2nd thoracic somite as broad as cephalic somite, % as long, laterally 

 cut off almost squarely. 3rd thoracic somite only slightly narrower 

 than 2nd, though slightly longer. Laterally it is rounded. 4th 

 thoracic somite small, half as broad as, and K the length of, the 3rd, 

 with rounded, scarcely produced sides. 



5th thoracic somite of characteristic, trapezoid appearance, maximal 

 diameter surpassing that of 4th thoracic somite, curious shape appar- 

 ently resulting from fusion of basal segment of leg 5 with somite (fig. 

 156). I failed to observe a line of separation between these two parts, 

 and the fine seta, which usually occurs on the basal segment, is found 

 here at the extreme external margin of the somite, near the insertion 

 of the 5th leg. The "shoulder" of the somite is set with scale-shaped 

 teeth. 



Genital somite resulting from fusion of abdominal somites 1 and 2, 

 slightly shorter than 5th thoracic somite, distinctly produced laterally. 

 The genital apertures are placed in the caudal wall of each swelling; 

 the genital plates are not visible from above and they are bordered by 

 3 nude setae each; one of these setae is lengthened. On the left side 

 of the genital somite a remnant of an egg sac is attached (figs, 15a,b). 



Kemaining abdominal somites gradually tapering, 3rd and 4th of 

 same length, half as long as genital somite. Anal somite 1% times as 

 long as somites 3 or 4, with a small, broadly rounded anal flap (fig. 

 156). 



Furcal rami parallel, shghtly asymmetrical, that on left side being 

 slightly larger. They taper slightly near the apex and are about IK 

 times as long as the basal diameter. Each ramus has 5 marginal 

 setae and 1 appendicular seta. Setae 3, 4, 5, and appendicular seta 

 short and fine, seta 2 on each side lengthened and thickened, reaching 

 the length of the abdomen. Seta 5 inserts halfway along the external 

 margin; the appendicular seta is placed on a slightly raised socle; its 

 place can best be judged from figure 156. Seta 1 is very small, placed 

 at the end of the internal margin, scarcely observable. There are no 

 spines, hairs, or teeth along the distal edges of the abdominal somites. 



Antennules 6-segmented, composed of 3-segmented basal part, with 

 indistinctly developed joints and more or less fused to ventral wall of 

 cephalic somite, and free 3-segmented portion. Total length of 

 antennules % length of cephalic somite. Setation represented in 



646-471—64 5 



