REPORT ON THE AMPHIPODA. 713 



than the front one. The first joint mucli larger than tlie side-plate, larger than the first 

 joint of the preceding pair, longer than Inroad, widest below, the front margin unarmed 

 in the upper part, the hind margin slightly crenulate, the lower margin overlapping the 

 second joint, convex, smooth ; the third joint decurrent, with spines on the inner side of 

 the decurrent part, and a large one at the apex, this joint twice as wide as the small 

 fourth joint which it overlaps, but without the wide expansion seen in the two preceding 

 pairs ; all the joints of this limb except the first are shorter than those of the fourth 

 pair, the armature not very different. 



Pleopods. — The peduncle short, almost as broad as long, coupling spines very small ; 

 outer rami with thirteen to fourteen joints, with eighteen plumose setae on the first 

 joint ; the inner rami with eleven joints, the first joint broader at the base than its length, 

 narrowed rather abruptly ; the cleft spines three or four in number. 



Uropods. — Peduncles of the first pair equal in length to the outer ramus, which is 

 bordered with seven spines, and is longer than the inner, which has but two ; each has a 

 small indistinct nail ; second pair shorter than the first, peduncles very stout, longer than 

 the rami, outer ramus longer and stronger than the inner, with a row of four spines, the 

 inner without spines, but like the outer tipped with a small nail ; third pair in a lateral 

 view presenting the appearance of an equilateral triangle, with spines round most of 

 the upper side to the apex and without any perceptible rami. 



Telson not much longer than broad, of the shape of half an egg, the apical part 

 underneath set about with a collar of some eighteen spines, only those nearest the apex 

 projecting beyond the margin, each spine carrying an accessory thread ; an additional 

 group of spines near the apex is placed within the collar. 



Length. — The specimen in the position figured was three-tenths of an inch long, 

 with a depth at the centre of rather more than two-tenths. 



Locality. — Station 145, ofi" Marion Island, December 27, 1873; depth, between 50 

 and 75 fathoms. One specimen ; male (?). Dredged. 



Remarks. — The specific name refers to the place of capture. 



The species is distinguished from the others of the same genus by its much more 

 considerable bulk, and the greater solidity of the integument. From Acontiostonia 

 magellanicum it differs in numerous details of the armature of the joints and in some of 

 the proportions, l)ut resembles it in so many particulars that some doubt arises whether 

 Acontiostoma magellanicum may not simply be the young of Acontiostoma marionis. 

 They were, however, taken at Stations far apart ; it is, moreover, in the smaller form 

 that the mandibular spine-row appears to have the larger number of spines, and the 

 maxilliped-palp to have the finger and nail most developed. Both these forms are 

 distinguished from the other two species of the genus by the difference in the palp of the 

 first maxillse, as well as by the more developed finger of the maxilliped-palp. 



(ZOOL. CHALL. EXP. — PART LXVII. — 1887.) XxX 90 



