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



The Thorax. 



As in Hahhates, the thorax forms by far the largest part of the body, and increases in 

 width naore or less from the front to beyond the middle. In a similar manner two only 

 of the three segments which compose it can be made ont, the posterior two being coalesced. 



The Prethorax is much Ijroader than long, and narrower than the head with the 

 eyes. The Pronotum has the front margin concave between the eyes, then obliquely 

 founded to the posterior angles ; the anterior angles excavated to receive the eyes ; the 

 sides rounded and convex ; the posterior margin slightly concave ; and the disk rather 

 flat. The Prosternum is in the middle third rather flat or longitudinally convex, and the 

 outer third on each side is occupied by the large acetabula. 



The Mesonotum is a little wider in front than the pro thorax, and widens gradually 

 backwards; the front margin is slightly convex in the middle, and then slopes slightly 

 eoncavely forwards ; the sides are rounded and convex ; and the disk is also convex. 

 The Mesosternum has the disk rather flat, anteriorly sloping to the prosternmn. 



Between the mesonotimi and metanotum no suture is apparent. The metanotum 

 slopes backwards between the ridges leading to the hind legs. No part of the meta- 

 thorax is visible below. The hind margin of the mesosternum is widely concave. 



The Abdomen. 



The structure of the abdomen is rather difficult to make out as regards the exact 

 point above where the thorax ends and the abdomen begins, or whether any of the 

 abdominal segments are covered by the integuments of the thorax. 



The Abdomen of the Male. 



On the dorsal surface in the male (PI. II. fig. 4 $ ah. cf., G $ ah. a.) one segment 

 appears to be covered, as its front margin is obscure. The front margin of the second 

 segment is angulated, the hind margin slightly concave, and the length in the middle is 

 three times the length at the sides. The third to the sixth segments have nearly straight 

 hind margins, the third segment being the longest of these. All the segments have a con- 

 spicuous connexivum, which is erect, and perj)endicular to the segments. It is widest 

 opposite the tliird segment, and thence decreases in width anteriorly and posteriorly. The 

 abdomen itself slopes backwards to the end of the fourth segment, and is then sub- 

 horizontal. Below, the male abdomen (PL II. fig. 4 $ ah. h., 6 $ ah. h.) is convex, with 

 six ring-like segments, whose hind margins arc concave. The first segment has the sides 

 mostly hidden by the mesosternum, and has in the middle a conspicuous perforated 

 tubercle as in Halohates. 



