108 THE VOYAGE OF H.M.S. CHALLENGER. 



Setella, Dana. 

 Setella, Daua, Crust. U. 8. Expl. Exped. (1852) 



Body extremely slender, almost linear, and bearing beneath the front of the head a 

 short and broad but sharply-pointed beak-like appendage. Head and first thoracic 

 segment coalescent. Anterior antenna? slender, bearing on the fourth joint an (olfactory ?) 

 appendage; posterior antenna? unbranched. Mouth-organs excessively minute. Mandible- 

 palp rudimentary. Maxilke and first pair of foot-jaws short and uncinate; second pair 

 of foot-jaws larger, and forming a clawed hand. Fifth pair of feet foliaceous. Caudal 

 seta? very long. 



Setella gracilis, Dana (PI. L. figs. 1-10). 



Setella gracilis, Dana, Crust. U. S. Expl. Exped. (1852), p. 1198, pi. lxxxiv. fig. 3, a-g. 



Length, 1-1 8th of an inch (l'4 mm.). The head is tapered towards the front, and bears 

 a stout, lancet-shaped rostrum. Abdomen in the female four- in the male five-jointed ; 

 margin of the penultimate segment finely pectinated; caudal segments slender, as long as 

 the three preceding abdominal segments ; principal seta? two, the innermost very long, 

 more than equalling the length of the whole body of the animal, the outer seta about as 

 long as the caudal stylet; both are finely aculeated through their entire length. Anterior 

 antenna slender and very sparingly setiferous, that of the female eight-jointed, about as 

 long as the cephalothorax ; that of the male (fig. 2) geniculated, slightly swollen above the 

 middle, and terminating in a slender slightly falciform joint ; posterior antenna (fig. 3) 

 three -jointed, simple, bearing at the apex three small subequal seta?, and two much smaller 

 marginal hairs. Mandible (fig. 4) very small and feebly toothed at the apex; palp 

 consisting of one small seta; maxilla (fig. 5) simple, subhamulate, without a palp; 

 anterior foot-jaw (fig. G) provided with a stout curved apical seta, and with two or three 

 marginal unisetiferous processes ; posterior (fig. 7) elongated, much larger than the 

 preceding, two-jointed, bearing at the apex a short curved claw, and on tbe middle 

 of the inner margin of the second joint a brush-like tuft of small fine hairs. First four 

 I lairs of feet long and slender (fig. 8), two-branched, the branches nearly equal, three-jointed; 

 fifth pair rudimentary, each branch consisting in the female (fig. 10) of a single joint, the 

 apices of both and the outer margin of the outer branch being setiferous ; in the male 

 (fig. 9) the inner branch is represented only by a couple of small seta?. 



Of this interesting genus Dana has described five species, some of them, perhaps, of 

 doubtful validity ; Claus one species, Setella messinensis, from the Mediterranean, and 

 Boeck one, Setella norvegica. The Challenger specimens agree most closely with Dana's 

 Setella gracilis, but the differences between this species and Setella tenuicornis appear to 

 be of the very slightest character. 



