340 BULLETIN 15 8, UNITED STATES NATIONAL MUSEUM 



Female. — Metasome elliptical, about twice as long as wide ; cephalic 

 segment three-fifths of the metasome length, squarely truncated an- 

 teriorly; fifth segment fringed with cilia on its lateral margins. 

 Urosome less than half the length of the metasome ; genital segment 

 only slightly dilated anteriorly; caudal rami short and slightly di- 

 vergent, outer margin without spines, outer seta near the center. 

 First antennae reaching the end of the third metasome segment, the 

 last three segments with a narrow lateral membrane. Outer exopod 

 spines on last segment of the first four legs 3, 3, 3, 2 ; fifth leg trilo- 

 bate, inner spine little shorter than outer and sparsely dentate, 

 middle seta elongate and borne on the tip of 

 a conical process. Anterior portion of semen 

 receptacle made up of two transversely S-shaped 

 canals, fused at the center into a longitudinal 

 stalk; posterior portion composed of a rounded 

 sack on each lateral margin of the segment, 

 connected by a transverse stalk, which joins 

 the longitudinal one from the anterior portion. 

 Total length, 0.4-0.7 mm. 



Male. — Smaller than the female, the cephalic 

 segment relatively shorter and rounded ante- 

 riorly; urosome more than half the length of 

 the metasome, 5-segmented; genital segment as 

 wide as the fifth segment anteriorly, but nar- 

 rowed posteriorly and no longer than the basal 

 abdominal segment; the four abdominal seg- 

 ments about the same length and width ; caudal 

 rami no longer than anal segment, divergent. 

 First antennae twice geniculate, the middle section scarcely enlarged ; 

 second antennae, mouth parts, and first four pairs of legs as in the 

 female; fifth leg 3-lobed, the inner spine longer and stouter than in 

 the female. Total length, 0.35^0.6 mm. 



Remarks. — Marsh said of this species : " Its characteristic habitat 

 is lakes rather than pools," but Pearse added : " It occurs in all situa- 

 tions from great lakes and rivers to temporary puddles of but a few 

 weeks' duration." ^^ It is nowhere abundant. 



Figure 202. — Eucyclopa 

 prasinus: a. Female, 

 dorsal (after Sars) ; 



b, female, fifth leg; 



c, male, fifth leg 



Genus ECTOCYCLOPS Brady, 1904 



Body short and stout; metasome elliptical, one-half longer than 

 wide, with epimeral plates on the second, third, and fourth segments ; 

 urosome stout, about half as long as metasome, 4-segmented in fe- 

 male, 5-segmented in male ; caudal rami short and stout, inner caudal 

 seta twice as long as outer. First antennae 10-segmented, first and 



" Bull. Illinois Lab. Nat. Hist, toI. 5, p. 58, 1897. 



