152 
Psyche 
[June 
to determine. It may serve as an “evaporating area” 1 for the secre- 
tion which emerges from the ostiole; unlike the smooth “evapo- 
rating surfaces” on the mesothoracic epimera of Hesperocorixa 
and Diaprepocoris, however, the groove of Micronecta bears short 
hydrofuge hairs similar to those on the rest of the ventral portion 
of the episternum. 
In both Hesperocorixa and Micronecta the lateral boundary 
between the mesothorax and metathorax projects anteriorly, as 
in Diaprepocoris. In Micronecta it forms a flap-like internal pro- 
jection (Fig. 19, II-III) which overlaps the trachea of the meta- 
thoracic spiracle (S III); the flap is similar to, but longer than, that 
of Diaprepocoris. Externally the lateral intersegmental boundary 
of Micronecta, like that of Diaprepocoris, forms a faint line (Fig. 16, 
II-III) which reaches anteriorly only as far as the level of the spiracle 
S III). In Hesperocorixa the boundary projects farther anteriorly, 
beyond the level of the spiracle (Fig. 17) and forms only a low ridge, 
rather than a flap, internally (Fig. 20, II-III). 
The metathoracic spiracles of both Hesperocorixa and Micronecta 
lie on the mesothoracic epimeron, anterodorsal to the intersegmental 
boundary and ventral to the mesothoracic scolopophorous organ. 
The fine structure of the spiracle and sense organ are described on 
pp. 161 and 164. 
E. Thoracico-Abdominal Region 
I. Typical Hydrocorisae 
The typical structure of the lateral thoracico-abdominal region 
of Hydrocorisae is diagrammed in Figs. 14 A and 21. The meta- 
thoracic epimeron (EM III) is relatively smaller than the meso- 
thoracic one and has a quite different shape. Anteriorly, beneath 
the hindwing, it is narrow; in the postalar region it broadens and 
joins the metathoracic postnotum forming a large, lateral postalar 
projecton (PP III). The metathoracic scolopophorous organ (SO 
III) lies anterodorsal to the projection. 
Posteromedial to the postalar projection, and separated from 
it by a pronounced fold, is a roughly triangular structure (TAS) 
which has been termed the “thoracico-abdominal sclerite” (Parsons 
'Although this term is not appropriate when applied to underwater insects, it is 
retained here because of its general use in the literature on terrestrial Heteroptera. 
