252 BULLETIN" 158, tlliriTED STATES NATION- AL MUSEUM 



In the first legs the exopod is shorter than the endopod and the 

 latter is tipped with two geniculate setae ; the endopod of the second, 

 third, and fourth legs is tipped with a single straight seta, and is 

 shorter than the exopod. The basal expansion of the fifth legs 

 reaches the tip of the distal segment, and has two equal apical setae 

 and a smooth inner margin. The distal segment is very small, twice 

 as long as wide and narrowed at its tip, with a long apical seta 

 and a shorter one on the outer margin. Total length, 0.7-0.75 mm. 



Male. — A little smaller and more slender than the female ; cephalic 

 segment about one-third the length of the metasome; second seg- 

 ment longer than the third, and fifth segment a little longer than 

 the fourth; urosome distinctly 5-segmented, anal segment only 

 three-fourths as long as penultimate segment; anal operculum with 

 smooth posterior margin. Caudal rami twice as long as wide, with a 

 stout apical spine, a slender but longer one at the inner distal corner, 

 three very unequal ones at the outer corner, and one on the dorsal 

 surface. First antennae twice geniculate, the terminal portion of 

 two segments equal in length, the fourth segment much longer than 

 either the third or the fifth ; second antennae like those of the female. 



In the first legs the exopod does not reach the center of the distal 

 endopod segment, its three segments diminish in length distally, 

 and it has no inner setae. Both segments of the first endopod are 

 fringed with hairs on their inner margins, and the end segment 

 carries two long geniculate apical setae. In the second legs the 

 two endopod segments have a row of stout spines running length- 

 wise on the anterior surface near the outer margin and no hairs on 

 the inner margin. The third and fourth endopods are unarmed 

 except for the single apical seta ; the second and third exopods have 

 no inner setae, the fourth exopod has one inner seta on the middle 

 segment and two on the distal segment. The apical setae of the 

 basal expansion of the fifth legs are very imequal and the inner 

 margin is denticulate. The distal segment does not reach the tip 

 of the basal expansion, is quadrangular in shape, as wide as long, 

 with four setae, the inner terminal one the longest. Total length, 

 0.6-0.7 mm. 



Remarks. — This species is nearly twice the size of the preceding 

 one, and can be further distinguished by the length and armature of 

 the caudal rami and the fifth legs. Its habits and habitat are very 

 nearly the same. 



Genus LEPTASTACUS T. Scott, 1906 



Body slender, elongate, cylindrical, with no demarcation between 

 the metasome and urosome; head fused with the first segment; ros- 

 trum well defined at its base; urosome 4-segmented in female, 5- 



