322 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 99 



1 female, U. S. N. M. No. 58530, collected at the 100-fathom line, 

 outside Chesapeake Bay, August 21, 1920. 



Types.— llolotype female, U. S. N. M. No. 85980; allotype male. No. 

 85979 ; locality, Beaufort Inlet, N. C. 



Diagnosis. — Possessing these characters of the subgenus Ditricho- 

 cori/caeus M. Dalil: Constituent of coastal plankton; small size; 

 rounded ventral process; leg 4 with its endopod bearing 2 setae, and its 

 second basal segment with a small protuberance inside ; spine of basal 

 segment of second antenna of female three times longer than that of 

 the second segment, only slightly longer in the male. Distinguished 

 by: Well-defined fourth thoracic segment; both sexes having the 

 genital segment approximately twice the length of the anal, with the 

 caudal rami divergent and longer than the abdomen in the female, 

 iibout three-fourths of its length in the male ; genital segment of female 

 inflated dorsally, that of both sexes with a medial ventral hook; 

 exopod of leg 4 having long spines on segments 1 and 3. 



DescrljHion. — Female (pi. 18, figs. 1, 2) : Total length about 1.10- 

 1.18 mm. Eyes small, Metasome composing 70 percent of the total 

 length of the body. Cephalic segment more or less distinctly sepa- 

 rated from thorax, equaling almost half of the total length of the 

 metasome. First thoracic segment overlying the second a consider- 

 able amount; the latter with a lateral hyaline flange ending in a 

 pointed tip. Wing of third segment broad, acutely pointed, reaching 

 just beyond the middle of the genital segment in dorsal view, inside 

 margin with a spinous point near the middle. Fourth thoracic seg- 

 ment entirely demarcated from third, wing with a rather large spinous 

 tip. Fifth segment hardly visible dorsally. 



Urosome composing 30 percent of total length of body. Genital 

 segment about twice the length of the anal, caudal rami longer than 

 both segments combined; proportional length of segments, lateral 

 view, ventral side: approximately 22:11:44. Genital segment (pi. 

 18, fig. 4) considerably inflated dorsally; distal margin with a fringe 

 of small spinules ventrally ; medial ventral hook small ; genital open- 

 ing witli a long plumose seta, reaching just beyond the end of the anal 

 segment. Caudal rami considerably divergent; with a lateral seta 

 distally and a terminal row of spinules; caudal setae 3 (pi. 18, fig. 3), 

 none as long as the ramus, the shortest spiniform, toothed on one 

 margin ; the others slender setae, of which the inner is the longer. 



First antenna having the first two segments broad, the others 

 slenderer; the fourth segment the longest, the terminal the shortest. 

 Segment 1 with two short setae. Second segment with eight setae, 

 two of which are as long as the segment is wide, and four of which 

 reach to the apex of the appendage. Segment 3 with two stalked 

 setae reaching beyond the terminus of the appendage. Fourth seg- 



