144 BULLETIN 15 8, UNITED STATES NATIONAL MUSEUM 



Female. — Metasoine three times as long as wide, head triangularly 

 pointed, the lateral angles forming hooks; corners of fifth segment 

 broadly triangular, reaching the center of the genital segment; 

 urosome asymmetrical, the genital segment produced ventrally on 

 the right side, and the right caudal ramus larger than the left 

 and turned outward; each fifth leg with two basipod segments, a 

 very short 1-segmented endopod, and a 2-segmented exopod eight 

 or nine times as long. Total length, 3-3.25 mm. 



Male. — Posterior corners of fifth segment very asymmetrical, the 

 right lobe produced into a fingerlike process that curves inward and 

 almost touches the first abdominal segment; genital segment with a 

 triangular projection on the right side at the posterior corner; 

 abdomen and caudal rami symmetrical; left fifth leg with a small 

 end segment tipped with a short claw, right leg with a terminal 

 quadrangular chela, the thumb very small, the finger curved and 

 spoon-shaped. Total length, 2.5-3 mm. 



Remarks. — This species is known to Norwegian fishermen as " blue- 

 bait," and its presence in the fiords indicates the approach of herring. 

 As noted by Sars it has the habit of swimming near the surface and 

 often jumping out of the water. Wheeler and Fish agree that it 

 appears in the present area only after prevailing south winds. The 

 modified antenna of the male is carried pointing straight in front 

 of the body, and this with its indigo-blue color enables one to dis- 

 tinguish the species readily. 



Genus LABIDOCERA Lubbock, 1853 



Head separated from first segment, with or without lateral hooks, 

 and with one pair of dorsal cuticular lenses ; fourth and fifth segments 

 fused, the corners produced into pointed lobes ; urosome 2- or 

 3-segmented in female, 4- or 5-segmented in male; genital segment 

 and sometimes the caudal rami asymmetrical in the female, but sym- 

 metrical in the male ; first four pairs of legs with 3-segmented exopods 

 and 2-segmented endopods; fifth legs biramose in female, right leg 

 of male uniramose with a chela, left leg often with a rudimentary 

 endopod. 



KEY TO THE SPECIES 



FEMALES 



1. Head with a distinct median crest ; corners of fifth segment sym- 



metrical, but urosome very asymmetrical acutifrons (p. 145) 



Head without a median crest; urosome symmetrical 2 



2. Corners of fifth segment angular but not produced ; endopods 



of fifth legs mere knobs, less than one-fourth as long as 



exopods nerii (p. 146) 



Corners of fifth segment produced into acuminate lobes ; endo- 

 pods of fifth legs more than one-half as long as exopods aestiva (p. 147) 



