1050 THE VOYAGE OF H.M.S. CHALLENGER. 



Second Perseopods. — The side-plates directed forwards like the three preceding pairs, 

 the front margin nearly straight ; the long lower margin very slightly fringed, sloping 

 rather sharply upwards, and almost continuous with the short piece of the hind mai'gin 

 which slopes sharply forward below the prominent angle of the excavation, which is 

 deeper than broad. The branchial vesicles and marsupial plates much as in the preceding 

 segments. The first joint reaching a little below the side-plates, the hind margin fringed, 

 except at the upper part, with many plumose setae, the front margin free above for a 

 short space, then armed with spines, and below with plumose setae ; the second joint 

 bearing four long plumose setae on the hind margin ; the third joint longer than in the 

 first perasopods, densely fringed on both margins ; the fourth joint as in the preceding 

 pair ; the fifth joint more than twice as long as the fourth, the three setae of the hinder 

 margin being on its upper half; the finger very little longer than the two preceding 

 joints united. 



TJiird Perasopods. — The side-plates broad, not very deep, the front lobe deeper than 

 the hinder, both unfringed. The branchial vesicles not large, directed more downwards 

 than forwards. The marsupial plates short and narrow, with seven long setae. The first 

 joint large, its front margin forming a great bend, what may be called the angle of the 

 curve being nearer the distal end than the base ; along some of the lower part plumose 

 setae project from the inner surface, along the upper part there are spinules ; the double 

 hind margin is in each case nearly straight above and bent below ; the short second joint, 

 which is partially overlapped in front by the first joint, has one or two apical spinules ; the 

 third joint has three very slender spines on the convex front margin, a strong bent spine 

 at its apex, and a spinule at the apex behind ; the fourth joint is straight, much longer 

 than the fifth, or than the two preceding joints united ; it has along the front margin 

 and apex thirteen long slender spines, distally pectinate, one at the apex being thicker 

 than the rest ; near the smooth hind margin are some minute surface spines, its slightly 

 produced apex carrying the usual mixed group of spines, one nearly as long as the 

 following joint, distally denticulate, three others shorter in various degrees, of the same 

 character, three very short but stout, three long and very slender ; the fifth joint is 

 narrow, and has on the serrate front border sixteen long and slender spines, two rather 

 stronger on the produced apex, and on the hind margin two spinules ; the minute 

 upturned finger has two or three dorsal denticles. 



Fourth Perseopods. — Side-plates small, with a couple of setae on the hinder part of the 

 lower margin. The branchial vesicles small, bent down and a little forwards. The first 

 joint of the limb shaped as in Ampelisca chiltoni; on the most prominent part of the 

 front margin there are seven plumose setae close together ; on the surface behind there 

 are many slender setae remote from the margin ; the second joint has an apical spine and 

 two spinules in front ; the third has three slender spines along the scarcely convex front 

 margin, and at its apex a stronger spine and two spinules, also a small spine at the apex 



