460 BULLETIN" 15 8, UNITED STATES NATIONAL MUSEUM 



similarly formed, except that the triangular claw has no spines on 

 its outer margin. The basal segment of the maxilliped is not swollen 

 so much and the terminal claw is not so long. The arrangement of 

 the spines and setae on the three segments of the swimming legs is 

 as follows: First exopod, 1-1, 1-1, 2-4; first endopod, 0-1, 0-1, 0-6; 

 second exopod, 1-1, 1-1, 3-4; second endopod, 0-1, 0-1, 1-4; third 

 exopod, 1-1, 1-1, 3-4; third endopod, 0-1, 0-1, 1-4; fourth exopod, 

 1-1, 1-1, 3-4; fourth endopod, 0-1, 0-1, 1-4. On the terminal endo- 

 pod segment of the second, third, and fourth legs the spine is between 

 the two outer setae and is terminal rather than on the outer margin, 

 as in the preceding species. Total length, 13.6 mm. Fused fifth 

 and genital segment, 9.5 mm. long, 1.15 mm. wide. Ovisacs, 14 mm. 

 long. 



Remarks. — This species can be recognized by its exceptional size, 

 the body plus the ovisacs being 25 mm. in length. It is possible 

 that the great blue shark is its only host, but more probable that it 

 will be found also upon the gills of other large sharks. 



Genus NEMESIS Risso, 1826 



FeTTude. — Head fused with first segment, carapace oval or elliptical 

 and longer than wide ; second, third, and fourth segments wider than 

 carapace, each covered with a dorsal plate the sides of which curve 

 around onto the ventral surface. Fifth segment usually reduced in 

 width, its dorsal plate just reaching either lateral margin; genital 

 segment smaller than the fifth segment; abdomen narrower but 

 longer than the genital segment, 2- or 3-segmented; caudal rami 

 minute and armed with short spines. First antennae 10- to 15-seg- 

 mented, filiform; second antenna uncinate; maxillipeds huge, project- 

 ing far beyond the carapace, uncinate ; first 4 pairs of legs biramose, 

 rami 2-segmented, fifth pair uniramose, 1- or 2-segmented. 



Male. — Carapace elliptical; second, third, and fourth segments as 

 wide as carapace or wider and not curved over ventrally; fifth seg- 

 ment narrower and much shorter than the fourth; genital segment 

 enlarged ; abdomen 3- or 4-segmented, the segments diminishing back- 

 ward; caudal rami differing considerably in size, with or without 

 plumose setae ; antennae, mouth parts, and swimming legs like those 

 of the female. 



KEY TO THE SPECIES (FEMALES) 



1. Fifth segment as wide as fourth ; abdomen 2-segmented ; sinuses 



between thoracic segments deep lamna (p. 461) 



Fifth segment mucli narrower than fourth ; abdomen 3-seg- 

 mented ; sinuses narrow and shallow 2 



2. Second segment with a notch on each lateral margin; fourth 



segment with lobes at posterior corners atlantica (p. 463) 



Second segment with smooth lateral margins, no notches; fourth 



segment without lobes at posterior corners pallida, new species (p. 464) 



