2298 CRUSTACEA. 



Plate 84, fig. 2 a, animal, enlarged ; a', appendage to beak. 



Atlantic Ocean, latitude 5° north, longitude 22° west, October 22, 

 1838. 



Length, one-twenty-fourth of an inch. Nearly colourless, except 

 the deep red of the stomach and intestine. The caudal stylets are 

 about as long as last three abdominal joints, and the setae are sca- 

 brous. 



This species closely resembles the preceding, and was at first sup- 

 posed to be the male of it. This view is perhaps favoured by the 

 difference in the abdominal appendages. But we deem it more pro- 

 bable that they are distinct, judging from the antennae, the two basal 

 joints in the longicauda being no stouter than the following; more- 

 over, the third joint is much less than twice the second in length, and 

 the first half the second ; while in the & tenuicornis, the third is more 

 than twice the length of the second. Moreover, the caudal setae are 

 much the longest in the longicauda. 



Setella gracilis. 



Feminse : — Antennas anticw gracillimce usque ad hasin, rectos, infer sese 

 prope 130° divaricatce; articulo primo obsolete, secundo quartum. 

 eequante et dimidio tertio longiore, quarto non arcuato. Digitus pedis 

 antici dimidio articulo secundo longiore. Setce caudales corpore fere 

 duplo longiores. 



Female: — Anterior antennae very slender even at base, straight, 

 angle of mutual divergence 130°, first joint obsolete, second as 

 long as the fourth and longer than half the third, fourth not arcuate ; 

 finger of first pair of feet longer than half the second joint; caudal 

 setae nearly twice as long as the body. 



Plate 84, &g. 3 a, side view, enlarged; b, back view, showing the 

 appearance swimming ; c, appendage to beak ; d, extremity of a max- 

 illa; e, first pair of legs; /, abdominal appendages; g, spinous cha- 

 racter of caudal setae. 



