COPEPODS OF THE WOODS HOLE EEGION 259 



each with two longer and three very short setae at the apex, and a 

 short one on the outer margin near the base of the ramus. The long- 

 est apical seta is shorter than the three abdominal segments combined. 



The three basal segments of the first antenna combined are three 

 times as long as the three terminal segments ; the second segment is 

 the longest and is armed with two large doubly pectinated setae, 

 one on the dorsal and one on the ventral surface, near the posterior 

 margin. The fourth segment is very short, but its aesthetask is 

 elongate and slender; the terminal segment is armed on its posterior 

 surface with a curved clawlike spine, which carries a row of slender 

 spinules of unequal length along its posterior margin. 



The terminal segment of the endopod of the second antenna is only 

 half the length of the basal segment, and has a transverse row of stiff 

 spinules on its dorsal surface near the tip. At the apex are two broad 

 lamellar spines, the outer one pectinated on its anterior margin, the 

 inner one smooth. The exopod is as wide as long, with three terminal 

 and one lateral setae, and is attached to the side of the basal endopod 

 segment at its center. The maxilliped is rather long and slender, its 

 terminal claw shorter than the second segment ; chewing blade of the 

 mandible with an angular outer process, palp rudimentary, without 

 any trace of an outer ramus. 



The outer margins of the exopod segments of the first four pairs 

 of legs are fringed with spinules in addition to the spine at the distal 

 corner, and the end segment has three unequal apical setae ; there are 

 no inner setae. The endopods are armed only at the apex of the end 

 segment ; the first endopod has three setae, the middle one more than 

 twice the length of the other two. The second endopod has four 

 setae, the outer and inner ones very short; the two middle ones and 

 the three apical setae of the exopod are elongate-flagellate, enlarged 

 at the base and densely tufted with cilia at the tip. The third endo- 

 pod has two equal plumose setae, the fourth endopod has two stout 

 spines and two short setae. 



The two segments of the fifth legs are completely fused into a 

 broad lamina, covered on its ventral surface near the base by trans- 

 verse rows of spinules. The two laminae meet and are fused across 

 the midline ; each carries 10 large setae, the bases of which are swol- 

 len into broad laminae that almost touch one another, and cover 

 practically the entire ventral surface of the fifth segment. The 

 plumes on these setae are confined to the distal tapering shafts of the 

 setae. The meeting point of the distal segment and the basal ex- 

 pansion is indicated by a narrow invagination between the fifth and 

 sixth setae, and there is also a well-defined outer process at the 

 base of the lamina on the outside. The exceptional structure of 

 these legs has given rise to the generic name, which signifies " the 

 fifth in order." Total length, 0.4-0.45 mm. 



