328 BULLETIN 15 8, UNITED STATES NATIONAL MUSEUM 



Female. — Metasome oval, a little more than half as wide as long; 

 fifth segment not produced laterally; urosome two-thirds as long as 

 the metasome; genital segment only slightly widened anteriorly, but 

 quite protuberant on the ventral surface. Caudal rami as long as 

 the last two abdominal segments, outer seta near the tip of the ramus. 

 First antennae 11-segmented, scarcely half the length of the cephalic 

 segment, the basal segments enlarged more than in varicans. Rami 

 of first four pairs of legs 2-segmented, fourth pair smaller than the 

 others, the outer apical spine of its endopod very small and rudi- 

 mentary. Basal segment of fifth leg entirely fused with the body, 

 distal segment very small and tipped with a filiform seta without 

 any trace of a lateral spine. Semen receptacle transversely elliptical 



and occupying nearly the entire 

 width of the genital segment. Total 

 length, 0.5-0.8 mm. 



Male. — Body more slender than in 

 the female; cephalic segment not so 

 long as the rest of the metasome ; fifth 

 segment produced laterally ; urosome 

 more than three-fifths as long as the 

 metasome ; genital segment with 

 straight lateral margins; the four 

 abdominal segments diminishing both 

 in width and length backward; cau- 

 dal rami as long as the last two seg- 

 ments combined, four times as long 

 as wide, the outer seta near the tip. 

 As in the female, the two apical 

 setae are subequal and much shorter 

 than the urosome. First antennae 

 11-segmented, not strongly hinged, the terminal portion composed of 

 two elongated segments, the end segment distinctly longer than the 

 preceding segment, the two combined longer than the middle sec- 

 tion of the antenna; sixth and seventh segments not swollen. Sec- 

 ond antennae, mouth parts, and swimming legs like those of the 

 female ; fifth legs also the same ; sixth legs represented by two setae 

 at each posterior corner of the genital segment. Total length, 

 0.4-0.7 mm. 



Remarks. — This species may be recognized by the 2-segmented rami 

 of the swimming legs, the 11-segmented first antennae, and the sub- 

 equal apical setae on the caudal rami. When alive it can be picked 

 out at once by its peculiar color. It is widely distributed but does 

 not seem to be abundant anywhere. 



Figure 195. — Microcyclops hicolor: a, 

 Male, dorsal ; b, male, fifth leg ; c, 

 male, first antenna 



