1976] Parsons — Morphology of Corixidae 159 
The thoracico-abdominal boundary is marked dorsally by the 
third phragma (Fig. 23, 3PH). The lateral part of the phragma 
becomes continuous with a low ridge (IR) which bends postero- 
medially. The bending is less abrupt than in Diaprepocoris and 
the intersegmental ridge does not adhere to the inner wall of the 
epimeral lobe like that of Diaprepocoris. It extends along the 
dorsal edge of the outer wall of the lobe as far as Point P. The 
narrow, flange-like external wall of the ridge is continuous with 
the posttergite of the third phragma and forms, like the latter, an 
attachment for the thoracico-abdominal membrane (TAM). The 
first abdominal spiracle (Figs. 16 and 19, S 1) lies in the thoracico- 
abdominal membrane immediately dorsal to the narrow flange. 
Although the spiracle is clearly visible under the stereoscopic and 
scanning electron microscopes, neither of these techniques revealed 
whether Micronecta possesses metathoracic or first abdominal 
scolopophorous organs. 
Posteromedial to Point P the intersegmental boundary appears 
to lie anterior to the base of the muscle process. The process (Fig. 
23, MP) is larger and flatter than that of Diaprepocorix and is 
separated from the second abdominal segment only laterally. 
Medially its crest is directly continuous with the second abdomi- 
nal antecosta (AC2), and its anterior and posterior surfaces thus 
appear to represent the first and second abdominal segments re- 
spectively. As in Diaprepocoris a muscle arises on its anterior 
surface and attaches dorsomedially on the first abdominal tergite. 
IV. Hesperocorixa 
The metathoracic epimeral lobe of Hesperocorixa was described 
and termed the “thoracico-abdominal sclerite” in a previous paper 
(Parsons 1970), but its homologies were not clear until the present 
investigation. 
The lobe (Fig. 24, EML) is relatively larger, both dorsoventrally 
and anteroposteriorly, than its homologues in Diaprepocoris and 
Micronecta. Its outer wall is anteriorly dilated and has a short 
anterior extension which fits against the wing-anchoring ridge of 
the episternum (W), as in Micronecta. From this extension a hori- 
zontal groove extends posteriorly along the outer wall; the edge 
of the forewing fits into this groove, which divides the outer wall 
of the lobe into dorsal and ventral portions. The ventral portion 
(EML; “thoracico-abdominal lobe” of Parsons 1970) is convex 
