segment has 3 external spines, 5 Internal setae, 

 and 1 slender terminal spine. Each of the first 

 and second endopodal segments has 1 internal 

 seta. The third segment has 1 external seta, 2 

 internal setae, and 2 terminal setae. The fifth 

 pair of legs is lacking. 



Description of Fifth Copepodid Female 



The total lengths of 42 specimens range from 

 5.47 to 6.14 mm. The prosome is about 7.8 times 

 as long as the urosome. The body shape (plate 

 2, figs. 14 and 15) resembles that of the adult 

 female. The genital segment shows a distinct 

 ventral swelling (plate 2, fig. 16), but is not 

 so strongly swollen as that of the adult female, 

 and lacks the genital opening. 



The segmental composition of the antennule 

 is exactly like that of the adult female. The 

 setal arrangement appears to be the same. The 

 antennae, masticatory appendages, and the 

 swimming legs are all similar to those of the 

 adult female, but the internal lobe of the second 

 endopodal segment of the antenna has 7 long 

 setae instead of 8, and the second to fourth 

 endopodal segments of the maxilliped have 3, 

 2, and 3 setae instead of 4, 3, and 4. 



Description of Adult Male 



The adult male was described from a single 

 specimen. The total length is 6.00 mm. ; the 

 ratio of the prosome to the urosome is about 

 6:1. The forehead in dorsal view (plate 3, figs. 

 1 and 3) is almost triangular, but the apex is 

 smoothly rounded and much less produced than 

 in the adult female. The first metasomal seg- 

 ment is fused with the cephalosome. The fourth 

 and fifth metasomal segments are not com- 

 pletely separated, but are fused in the ventro- 

 lateral regions (plate 3, fig. 2). The postero- 

 lateral corners of the metasome are smoothly 

 rounded. 



The urosome (plate 3, fig. 4) consists of 4 

 free .segments and the caudal furca, a complex 

 composed of the anal segment fused with the 

 caudal rami. The segments and caudal furca 

 have the following proportional lengths, from 

 anterior to po.sterior: 17:22:18:13:30. 



The genital segment is slightly produced on 

 the left side, and has a distinct genital opercu- 

 lum. The left caudal ramus is slightly larger 

 than the right. The second medial terminal seta 



on the left ramus is markedly stouter and much 

 longer than the others. 



The antennule (plate 3, fig. 2) has 24 free 

 segments, only the eighth and ninth of which 

 are fused ; the last 7 segments extend beyond 

 the caudal furca. The antenna (plate 3, fig. 5) 

 is very similar to that of the female but the 

 basis is stouter. 



The mandible (plate 3, fig. 6) differs from 

 that of the female in two respects : it is smaller, 

 and the mandibular blade is degenerated and 

 has a single spinelike tooth. The basis has 4 

 setae at the upper portion of the internal 

 margin, as does that of the female. The endopod 

 arises just distad of the midpoint of the basis 

 and has 2 setae on the first segment and 5 on 

 the second segment. 



The maxillule (plate 3, fig. 7), maxilla, and 

 the maxilliped (plate 3, fig. 8) are much smaller 

 than those of the adult female but resemble the 

 latter in shape and in details of setal 

 arrangement. 



The first to fourth pairs of legs are nearly 

 identical with those of the female. The left 

 and right fifth legs (plate 3, fig. 9) are both 

 uniramous. The left one is 4-segmented ; the 

 distal segment is tipped with a seta, and the 

 last two segments are fringed with hairs along 

 the inner margins. The segments in the left 

 fifth leg have the proportional lengths of 39: 

 21:14:26. The right fifth leg is also 4-seg- 

 mented, but the last 2 segments are incom- 

 pletely separated. The distal segment is tipped 

 with a seta, and the third segment has a small 

 spine on its inner edge. The right fifth leg is 

 short — it reaches about the middle of the sec- 

 ond segment of the left leg. The segments have 

 the proportional lengths of 48 :24 :28 (third + 

 fourth ) . 



Description of Fifth Copepodid Male 



The total length of 51 specimens ranges from 

 5.47 to 6.04 mm. The proportional lengths of 

 the prosome and urosome are 7.7:1. The gen- 

 eral body shape (plate 3, fig. 10) resembles 

 that of the fifth copepodid female. The head in 

 dorsal view (plate 3, fig. 11) has a triangular 

 frontal part that ends in a blunt point. The 

 urosome (plate 3, fig. 12) consists of 3 free 

 segments and the caudal furca. 



The antennule (plate 3, fig. 10) has 23 free 



CALANOID COPEPODS FROM NORTH PACIFIC 



537 



