334 



BULLETIN 15 8, UNITED STATES NATIONAL MUSEUM 



for the distal half. Third and fourth segments of second antenna 

 equal and twice as long as the second segment, which is coarsely 

 denticulate on its posterior margin. Outer apical spine of fourth 

 endopod much larger than the inner one and armed on its inner 

 margin with several large spinules in place of the usual teeth. Basal 

 segment of fifth legs quadrangular, fringed with spines on its inner 

 margin; distal segment shorter and narrower, its inner spine twice 

 the length of the outer. Posterior part of semen receptacle usually 

 bright red and tongue-shaped, with a narrow posterior median cleft 

 reaching beyond the center. Ovisacs pressed tightly against the sides 

 of the urosome. Total length, 2-4 mm. 



FiGDBB 198. — Macrocyclops fuscus: a, Male, dorsal ; i, male, first antenna ; c, 

 male, fifth leg ; d, female, apical spines of the fourth endopod 



Male. — Body short and stout; cephalic segment narrowed an- 

 teriorly and almost squarely truncated posteriorly, and nearly twice 

 as long as the rest of the metasome, its length to its width as 6:5; 

 second, third, and fourth segments wide and slightly produced at 

 their posterior corners into small blunt knobs ; fifth segment abruptly 

 reduced to half the width of the fourth, and partly concealed by 

 the latter; genital segment twice as wide as long and wider than 

 the fifth segment; abdomen 4-segmented, each segment two or three 

 times as wide as long; caudal rami as long as the last two abdomen 

 segments combined, the outer seta close to the tip. First antennae 

 l7-segmented and twice hinged, the middle section elongate and 5- 

 segmented, its proximal segments only slightly swollen. Total 

 length, 1-1.25 mm. 



Remarks. — This is one of the largest of our American species and 

 may be distinguished first by its size, then by its dark color, and by 



