140 THE VOYAGE OP H.M.S. CHALLENGER. 



The remaining segments of the thorax increase in length up to the fifth ; their width 

 increases up to the third, and thence diminishes gradually though not to any marked 

 extent. 



The three anterior segments of the thorax, including the rudimentary first segment. 

 are subequal in length as well as breadth to the head ; the second has a row of tubei < 

 across the median region, the third has a few similar tubercles; the other segments of 

 the thorax as well as the abdomen are smooth and free from any tubercles although 

 hairy in places. Just posterior to the articulation of the limbs in the third segment, 

 that is to say along the postero-lateral margin of that segment, is a short conical 

 spine; the antero-lateral margin of the succeeding segment has two such spines close 

 together, the outer being the larger. Between the third and fourth segments is a 

 considerable break, a deep lateral incision dividing them ; the postero-lateral margin 

 of the fourth has a stout mammilla-like process which answers to the postero-later.il 

 spine of the third. The fourth segment is separated by a moderately deep incision 

 from the fifth, which is closely applied to the sixth, the two together forming almost 

 a continuous piece, though the line of suture is evident enough; the fifth segment is, 

 as usual in this genus, divided by a median longitudinal furrow into right and left 

 halves ; the lateral margin of the fifth segment is divided by constrictions into three 

 areas, of which the median overlies the articulation of the limbs ; the sixth segment is 

 divided by transverse constrictions into three projecting areas, beneath the posterior of 

 which the limbs belonging to this segment arise ; the postero-lateral margin of this 

 segment, as of the fourth segment, is prolonged into a process. Between the sixth 

 segment of the thorax and the first segment of the abdomen is intercalated a small 

 segment of about the same length and width as any of the succeeding segments of the 

 abdomen ; it differs from them, however, in not being furnished with epimera ; nor has 

 it any trace of appendages ; the rudimentary condition of this segment, which appears to 

 be equally rudimentary in all species of the genus, is an embryonic character, inasmuch as 

 this segment in other Isopoda is the last to appear (cf. description of young of Eurycope 

 novse-zealandiw, p. 63). 



The abdomen measures a little more than one-fourth of the entire length of the body; 

 the segments of which it is composed gradually increase in length up to the fifth; tiny 

 are furnished with well-developed sickle-shaped epimera quite separate from each other ; 

 those of the first abdominal segment are considerably smaller than of those which follow ; 

 the epimera stand out from the body and are not compressed as in Anceus gigas; the 

 terminal segment of the abdomen has no epimera, and it terminates in a peculiarly notched 

 extremity. 



The antennas (PI. X. figs. 8, 9), resemble those of the preceding and other species of 

 the genus in almost every particular ; in both pairs of appendages, however, the flagellum 

 appeared to be a joint shorter than in Anceus yigas. 



