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



present, it seems best to keep them under one specific name. One of the localities given 

 by Dana corresponds pretty nearly with the Challenger Station No. 349. 



Machairopus, 1 n. gen. 



Cephalothorax broad and rather depressed ; abdomen five-jointed in both sexes. 

 Anterior antenna? nine-jointed ; inferior three-jointed, with a large three-jointed inner 

 branch. Mandible strong, and provided with a slender two-branched palp. Maxilla (?). 

 Foot-jaws three-jointed, the second pair uncinate and flexed in a geniculated manner. 

 Inner branch of the first pair of feet two -jointed, armed at the extremity with two broad 

 laminated or knife-like appendages in place of claws ; outer branch short, three-jointed, 

 and strongly setiferous, second, third, and fourth pairs having both branches three- 

 jointed ; fifth pair foliaceous, two-jointed. Eyes distinct and widely separated. 



In this genus the characters are intermediate between Idya and Scutellidium, the 

 antenna, foot-jaws, and mandibles agreeing with the former, while the feet are like those 

 of the latter genus. The only species is 



Machairopus idy aides, n. sp. (PL XLI. figs. 1-12). 



Length, l-20th of an inch (1'3 mm.). Cephalothorax much broader than and 

 separated sharply from the abdomen. Anterior antennae rather densely setiferous, geni- 

 culated in the male. The secondary branch of the posterior antenna (fig. 4) is stout, 

 and three- (or four- ?) jointed ; the mandible (fig. 5) is tapered towards the apex, and not 

 very strongly toothed ; the basal joint of the palp is long and slender, and the branches 

 are composed each of a single joint with five long setae ; the foot-jaws (figs. 6, 7) are 

 both three-jointed, but the second has a longer terminal claw, is more slender, and is 

 flexed upon itself between the first and second joints. The feet of the first pair are 

 exactly as in Scutellidium, the broad lamina and knife-like apical armature of the inner 

 branch being very characteristic (fig. 8) ; the outer branch is much shorter, and bears 

 several very stout plumose setae ; the last joint is very short and broad, and has five such 

 setae ; the first and second joints have each one or two ; the outer margins of both branches 

 are likewise densely fringed with short, rather rigid hairs. The other swimming feet 

 (fig. 9) have equal, three-jointed branches, with densely pectinated outer margins ; 

 marginal spines slender and lancet-shaped ; terminal spines long and slender. The basal 

 joint of the fifth foot in the female (fig. 10) is broad and bilobed at the apex, the outer 

 margin bearing a fringe of long, fine, and closely-set hairs, the inner margin less profusely 

 fringed in a similar way ; the apex of the outer lobe has three long, slender setae, the 

 inner lobe one long hair and a series of about eight small tooth-like setae ; the second joint 

 is long and subovate, has ciliated margins, and five long, unequal apical setae. The outer 



1 pxxxipx, a knife; vou;, a foot. 



