332 BULLETIN 15 8, UNITED STATES NATIONAL MUSEUM 



Female. — Metasome regularly elliptical, the width slightly more 

 than half the length ; cephalic segment almost twice the length of the 

 rest of the metasome; urosome slender, more than half the length 

 of the metasome; genital segment as long as the abdomen and 

 cylindrical; caudal rami shorter than the last two segments of the 

 abdomen combined, outer seta near the center of the ramus, longest 

 apical seta as long as the urosome. First antennae reaching the 

 posterior margin of the third thoracic segment; end segment bor- 

 dered by a hyaline membrane, sometimes serrate, sometimes with a 

 single semilunar sinus, or with four or five such sinuses. Distal 

 segment of fifth legs narrow, the two setae slender and elongate, the 

 inner one somewhat removed from the tip. Anterior portion of the 

 semen receptacle short and bilobed, extending across the segment, 

 posterior portion tongue-shaped, prolonged lengthwise of the seg- 

 ment. Total length, 1-1,5 mm. 



Male. — Much smaller than the female; cephalic segment longer 

 than the rest of the metasome, its length to its width as 5:3; second, 

 third, and fourth segments rather wide and slightly produced at the 

 posterior corners; fifth segment abruptly narrowed to the width of 

 the genital segment; abdomen 4-segmented, the segments diminish- 

 ing but little in length or width; genital segment as long as the first 

 two abdominal segments combined ; caudal rami longer than the anal 

 segment,' but not so long as the last two segments together, with the 

 lateral seta at the center of the outer margin. First antennae 17- 

 segmented and twice hinged, the terminal portion made up of two 

 elongated segments, the middle portion 4-segmented and enlarged at 

 its proximal end. First four pairs of legs not modified; fifth legs 

 like those of the female but somewhat smaller. Total length, 0.75- 

 0.9 mm. 



Remarks. — The list of ponds given above shows that this species is 

 universally distributed through the fresh water of the area. It was 

 not present in any of the brackish ponds but has been reported from 

 brackish water in India. As Marsh has pointed out, it is easily 

 recognized by the form of the caudal rami, since it is the only species 

 with the first antennae l7-segmented in which the outer seta of the 

 caudal rami is at the center. The elongate, subequal setae of the 

 fifth legs are also characteristic. 



Genus MACROCYCLOPS Claus, 1893 



Metasome obovate, boldly arched dorsally; fifth thoracic segment 

 no wider than the genital segment; urosome moderately stout; geni- 

 tal segment only slightly dilated anteriorly; caudal rami but little 

 longer than the anal segment. First antennae 17-segmented, reach- 

 ing the posterior margin of the third, or even the fourth thoracic 

 segment. Rami of first four pairs of legs 3-segm,ented„ end segment 



