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



Acontiostoma magellanicum, n. sp. (PI. XXXI.). 



Head almost entirely covered by the first perseon-segment and its side-plate ; back 

 round, animal compact ; postero-lateral angles of the first two pleon-segments well 

 rounded, of the third also rounded but forming almost right angles, with the lower margin 

 straight ; fourth segment mth a dorsal depression followed by a small hump overhanging 

 the very small fifth and sixth segments ; on each of the first four segments a dorsal hair 

 is visible. 



Eyes small, visible through the transparent side-plate ; each eye is composed of about 

 fifteen comparatively large ocelli. 



Upper Antennse. — First joint twice as long as broad or longer ; second joint nearly as 

 broad but much shorter, third joint nearly as long as second, narrowing distally ; flagellum 

 of four very short joints, successively narrower but scarcely shorter ; the first with two 

 long stout cylinders, the second and third each with one ; the fourth tipped with a tuft 

 of setfe ; secondary flagellum of two short joints. 



Lower Antennse not quite so long as the upper ; gland-cone prominent, blunt-ended, 

 third joint short, fourth longer than fifth, fifth almost as long as the small four-jointed 

 flagellum ; some spiniform setse on the terminal joints of the flagellum, also at the base 

 of the peduncle a curious parasitic growth, described below. 



Mandibles of the same shape as those described in Acontiostoma pepinii, but here 

 there is an undoubted secondary plate on the left mandible, small, strap-shaped, a little 

 expanded distally ; the spine-row consists of half a dozen small spines, followed by a long 

 furry tract of short cilia; the setae at the apex of the third joint of the palp have the 

 parasitic growth. 



Lower Lip with the forward lobes apically ciliated, very slightly dehiscent. 



First Maxillis. — Inner plate slender, tijsped with a long, straight seta ; outer plate 

 long and narrow, with seven or eight dentate spines closely set on the apical margin, with 

 a little group of cilia just below on the inner margin ; the unarmed palp appears to be 

 one-jointed, reaching with its point nearly to the base of the outer spines on the outer 

 plate, a little constriction below the point giving it in some points of view the appearance 

 of the nib of a pen ; the curved inner spine of the outer plate has from nine to ten lateral 

 denticles. 



Second Maxillse with both plates slender, the outer rather longer than the inner ; 

 each with eight or nine apical spines. 



MaxiUip)eds. — Inner plates short, ending in a long tooth which just projects beyond 

 the short first joint of the palp, and has a long seta fixed at its base ; outer plates 

 projecting beyond the second joint of the palp, inner border with a spine about midway, 

 some others within the margin on the outer surface near the narrowed apex ; the forward 

 part of the hinder margin scarcely serrate ; the third joint of the palp longer than the 



