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



has the appearance of a deep dish-cover ; the first perseon-segment much longer than the 

 second, forming in front a h^w narrow arch over the antennae ; behind it projects back- 

 wards with a rounded lobe beyond its own side-plate ; the first three segments of the 

 pleon with a sharp, very slightly elevated, dorsal carina on the distal end of each, the 

 first two with the postero-lateral angles rounded, the third having them squared ; 

 the fourth segment with a dorsal depression, the afterpart with an elevated carina 

 produced a little backwards ; the two following segments very small. 



Eyes comjaaratively large, oval, with the front margin somewhat flattened, situated 

 near to the slightly convex medio-lateral margin of the head, dark, with the usual light 

 rim. 



Ui^per Antennw. — First joint large, cylindrical, equalling in length the rest of the 

 antenna ; second joint almost as long as the flagellum, third narrower and rather shorter 

 than the second ; flagellum of seven short joints with stout cylinders, five or six on the 

 first joint, which is not greatly longer than the second ; secondary flagellum slender, of 

 two joints, the first about as long as the first of the primary, the second minute. 



Loiver Aiitennse. — The gland-cone very prominent, standing at right angles to the 

 third joint ; fourth joint much longer than the fifth, a little curved, and expanding a 

 little distally, some setae on the side and at the apex ; fifth joint not rj^uite so long as the 

 tapering, seven-jointed flagellum. 



Upper Lip broad at the base, centrally ridged, narrowing gradually at first, towards 

 the end more abruptly, as if to end in a broadly rounded point ; in our specimen the apex 

 shows a serrate emargination, but whether this is normal or due to fracture I cannot say 

 for certain ; there is furring within and on either side of the apex, also the inner plate, 

 which does not quite reach the apex of the outer, has its own rounded apex densely 

 furred. 



Mandibles very long and narrow and straight ; the cutting edge smooth ; the 

 secondary plate of the left mandible not perceived, probably very small ; spine-row of 

 three or four small spines, followed by a long furry tract of cilia, the only representative 

 of a molar tubercle ; above is a projection corresponding apparently to the " articular 

 condyle " of Schiodte, and to the part of the mandible of Acidostoma ohesum which Lillje- 

 borg, on Lysianassa magellanica (pi. v. fig. 56), calls the molar tubercle, but which 

 from its position can scarcely have an5rthing to do with that organ either in origin or 

 function ; far to the rear is placed the small three-jointed palp, the base of the mandible 

 being a little dilated behind it ; the first joint of the palp comparatively long, with one 

 seta attached near the outer apex ; the second joint with two pectinate setae or spines at 

 the outer apex ; the third joint slender, curved, as long as the second, with numerous 

 adpressed cilia, and at the apex two unequal pectinate spines. 



Loiver Lip strongly ciliated on the forward lobes, which are much narrowed distally ; 

 the mandibular processes also ciliated. 



