REPORT ON THE PELAGIC HEMIPTERA. 29 



the hind margin between the posterior angles is also concave, but often only slightly so, 

 and in every case less concave than the front margin. The sides are a little oblique, so 

 that the pronotum is a little wider behind than in front ; gently rounded and convex, 

 with the anterior and posterior angles also rounded. The disk is somewhat convex, or 

 flat, somewhat slightly raised longitudinally in the middle line, or with a finely impressed 

 line there. On each side of the middle line there is frequently a more or less distinct 

 small transverse fovea situated a little behind the front margin ; in some cases there is a 

 larger fovea on each side, situated behind the anterior fovea. These foveas may be of 

 post-mortem origin. One species is described as being provided with three longitudinal 

 furrows. Sometimes the pronotum is depressed in the middle of the hind margin. Its 

 shape varies a little in the sexes. 



The Prosternum is rather shorter than the pronotum, the front margin is less con- 

 cave, and the hind margin is slightly convex. Of the disk the outer third on each side 

 (except the extreme margin) is occupied from the front to the back by the large swollen 

 acetabula of the front legs. The middle third is more or less strongly elevated on the 

 longitudinal middle line. 



The acetabula, viewed from the side, are perpendicular or slightly oblique behind, 

 where they are highest ; and from the back to the front present a strongly convex out- 

 line. Viewed from the front they are somewhat triangular in outline. The opening of 

 the acetabula looks backwards, and a little inwards, and rests behind against the meso- 

 sternum. The anterior rim has a large triangular notch (PL I. fig. 8, ac), whose apex 

 reaches to within a short distance of the front margin of the prosternum. From its apex 

 a slit or suture proceeds to, or almost to, the front margin. 



Tlie Mesothorax and Metathorax. 



These two segments are coalesced, and together occupy frequently about three-fifths 

 of the entire length of the body. They form also by far the broadest and deepest part. 

 The suture between them is most frequently indicated merely by a sharp short trans- 

 verse impression (not always to be discerned) situated on each side within, and a little in 

 front of, the ridge leading to the hind legs. Below no part of the metathorax is visible. 



Tlie Mesonotum is more or less distinctly wider in front than the pronotum. The 

 front margin is convex in the middle, and then concave at each side to receive the 

 posterior angles of the pronotum ; the anterior angles are produced a little in a forward 

 direction. The sides are rounded and convex, and the width increases backwards — 

 varying a little according to species and sex — till the greatest width is attained at, or a 

 little before, or a little behind, the middle. The disk is frequently more or less convexly 

 swollen (more rarely nearly flat), and is highest in the middle anteriorly. Sometimes 

 there is a very fine impressed longitudinal central line. Posteriorly the mesonotum with 

 the metanotum slopes more or less rapidly backwards between the insertion of the legs. 



