REPORT ON THE PELAGIC HEMIPTERA. 31 



has never been found with elytra or wings, and has probably never possessed them, it will, 

 on the whole, be as well not to consider the plates in question to be rudimentary organs. 



Between the plates the thorax diminishes in width backwards, and is marked on each 

 side by transverse impressions, deepest at the sides, and rarely going across from one 

 side to the other. These impressions indicate the position of the first three segments of 

 the abdomen, which are covered by the integuments of the thorax. 



The Mesosternum is more or less flat. The anterior angles are somewhat tumid, and 

 have within them (at least sometimes), a short oblique furrow, in which lies the base of 

 the anterior trochanter. The hind margin is more or less widely and deeply concave. No 

 part of the metathorax is visible below. 



The Abdomen. 



The abdomen, viewed from above, is small, rather depressed posteriorly, and, as regards 

 the portion not concealed by the thorax, sub-triangular in outline, the apex of the triangle 

 having attached to it in the male the conspicuous lozenge-shaped third genital segment, 

 and in the female, being conical. The abdomen rarely reaches backwards much beyond the 

 trochanters of the hind legs. 



Including the genital segments, the abdomen consists of nine segments, of which the 

 first three are covered above by the metanotum, and the last three are the genital 

 segments. 



TJie Abdomen of the Male. 



Dorsal Surface. — (PL I. fig. 8, t y8). The hind margins of the first two (covered) 

 segments, when they can be traced across, are rather strongly concave, or even some- 

 times slightly angulated ; the hind margin of the third segment (coinciding with the 

 hind margin of the metanotum) is less concave, or sometimes nearly straight. These 

 three segments are longer in the middle than at the sides. Occasionally the suture be- 

 tween the second and third segments can be traced across the side plate (pleuron) men- 

 tioned in the description of the thorax. In most species the division between the third 

 and fourth segments is well defined on this plate. 



The fourth segment (the first free one) is usually the longest of the free segments, the 

 remaining two being rather shorter and subequal in length to each other. At the sides of 

 the basal segments there are sometimes slight indications of a connexivum (pleuron), but 

 owing to the position of the abdomen this is very inconspicuous and obscure. The genital 

 segments will be described separately. 



Ventral Surface. — (PL I. fig. 8, ^ ah. h.). All the six abdominal segments are uncovered. 

 The first five are very short, ring-like, subequal in length, and more or less retracted 

 within each other. The first is more or less covered at the sides by the mesosternum. 



