1976] 
Parsons — Morphology of Corixidae 
155 
Ranatra (Nepidae; Parsons 1972a), and the Corixidae examined 
here. 
The sternite and tergite of the second abdominal segment are 
joined laterally (Fig. 14 A). The anterolateral part of the segment 
projects anteriorly forming an abdominal projection (Figs. 14 A 
and 21, AP) upon which the edge of the forewing rests. The second 
abdominal spiracle, like the more posterior ones, is much smaller 
than the first abdominal one and lies in the ventrolateral part of 
the segment (Fig. 21, S2). 
All three of the corixids examined here differ from the typical 
plan in three major respects: (1) the evaginated lobe of the meta- 
thoracic epimeron is much larger than in other Hydrocorisae, 
(2) the metathoracic postalar region does not form a strong lateral 
projection, and (3) the first abdominal spiracle lies in the functional 
thoracico-abdominal membrane rather than in the metathoracic 
epimeron. The three insects differ mainly in the shape of the meta- 
thoracic epimeron and in the way in which it is joined to the ante- 
roventral part of the abdomen. 
II. Diaprepocoris 
The posterior part of the metathoracic epimeron of Diaprepocoris 
is diagrammed in Fig. 22. Unlike the thoracico-abdominal sclerite 
of typical Hydrocorisae (Fig. 21, TAS) it is not recessed on the 
body; its external wall is directly continuous with the postalar 
bridge, which does not project strongly laterally. The posterior 
part of the subalar membrane contains a small sclerite (SO III) 
which probably forms an attachment for the scolophore of a meta- 
thoracic scolopophorous organ. 
The epimeron forms a large, two-walled ventral lobe (Figs. 18 
and 22, EML) which extends posteroventrally from the metacoxal 
process (Fig. 18, PR; Fig. 22, heavy black dot). The metacoxal 
membrane (MM) attaches along the free dorsal edge of the inner 
wall of the lobe. The inner (medial) and outer (lateral) walls are 
joined anteriorly, ventrally, and posterodorsally; their apposed 
surfaces adhere closely to each other and are difficult to separate. 
The dorsal opening into the lobe extends from the coxal process 
to a point (Fig. 22, P) approximately midway between the level 
of the third phragma (3PH) and the anterior edge of the abdominal 
projection (Figs. 15 and 22, AP). Posterior to Point P the lobe 
projects posteroventrally, as a blind sac, ending just ventral to 
the anterior edge of the abdominal projection. 
