202 



BULLETIN 15 8, UNITED STATES NATIONAL MUSEUM 



Color. — Entire body dark bluish black except the dorsal surface 

 of the cephalothorax, which is light gray ; eye reddish or sometimes 

 bluish. 



Female. — Rostral projection fairly prominent and angular at its 

 tip; posterior margins of all the segments finely crenulated; genital 

 segment wider than the fifth metasome segment, a median division 

 indicated laterally; caudal rami nearly three times as long as wide, 

 the inner apical seta stouter than the others and about twice the 

 length of the rami. Exopod and endopod of first legs equal in 

 length, with smooth apical claws; fifth legs broadly foliaceous, ex- 

 tending beyond the center of the genital segment, the inner expansion 

 of the basal segment reaching the tip of the distal segment, with five 

 apical setae; distal segment with three outer and three apical setae, 

 _ the latter very slender. Total 



length, 1.4-1.6 mm. 



Mole. — Smaller than the female ; 

 first antennae stout and genicu- 

 late, the terminal portion very 

 short and curved. Endopod of sec- 

 ond legs with its second and third 

 segments fused and armed with 

 stout spines ; fifth legs much smaller 

 than those of the female, the inner 

 expansion of the basal segment 

 very short, with three unequal 

 setae, the middle one elongate, the 

 outer one minute; distal segment narrowed terminally, but carrying 

 six setae. Total length, 1.25-1.4 mm. 



Remarks. — As remarked by Sharpe, this is apparently a boreal 

 form that comes down into the present area from the north. When 

 alive it can be recognized at once by its very dark color combined 

 with its large size. 



Figure 133. — Thalestris gibba: a, Female, 

 fifth leg (after Sars) ; b, male, fifth 

 leg. (From R. W. Sharpe, Proc. U. S. 

 Nat. Mils., vol. 38, p. 418) 



Genus HALITHALESTRIS G. O. Sars, 1905 



Body elongate and subcylindrical ; urosome not sharply separated 

 from the metasome ; head fused with the first segment, small and de- 

 pressed; urosome 4-segmented, as large as metasome; caudal rami 

 unusually elongated and strongly divergent, the apical setae of 

 medium length. First antennae 9-segmented; exopod of second an- 

 tennae 2-segmented ; first four pairs of legs with 3-segmented rami ; 

 fifth legs 2-segmented, of medium size and foliaceous. One species 

 found here. 



