1976] 
Parsons — Morphology of Corixidae 
173 
performed by the hydrofuge hairs on the mesonotum rather than 
by lengthening of the pronotum. The presence of a long, strongly 
indented embolium appears to be related to the size of the partial 
supra-alar air store on that region. The embolium is longer and 
more sharply indented in Hesperocorixa (Fig. 10), in which the 
air layer extends beyond the nodal furrow, than in Micronecta 
(Fig. 9), in which the air extends only to the furrow. In Diaprepo- 
coris the supra-alar air store covers nearly all of the forewing rather 
than being confined mainly to the embolium, and the latter is only 
weakly indented (Fig. 8). 
Two previous works (Parsons 1970, 1974) have discussed the 
ways in which the pterothorax of Hesperocorixa differs from that 
of most other Hydrocorisae. Popov’s (1971) views on the phy- 
logeny of the three living subfamilies are supported by the fact that 
Micronecta shares more of these pterothoracic characteristics 
than does Diaprepocoris. In all three corixids the metathoracic 
spiracle faces directly onto the subalar air store rather than being 
concealed by a high lateral epimeral ridge (Fig. 14A, LR) as in 
most other Hydrocorisae. Diaprepocoris, however, possesses a 
low epimeral ridge (Fig. 15, LR) while the other two corixids lack 
the ridge entirely. All three insects possess a weakly developed, 
rather than a prominent, mesothoracic postalar projection and a 
modified mesothoracic scolopophorous organ. The latter is sim- 
plest in Diaprepocoris (Fig. 25) and most complex in Hespero- 
corixa (Fig. 27). Diaprepocoris differs markedly from the other 
two corixids in the shape of its mesothoracic lateral epimeral lobe, 
which resembles that of most other Hydrocorisae (Fig. 14A) rather 
than being widened and strongly curved dorsally (Fig. 14B). The 
metathoracic air trough is also poorly developed in Diaprepocoris; 
it is more pronounced in Micronecta (Fig. 16, AT) and is most 
highly developed in Hesperocorixa (Fig. 17, AT). 
The thoracico-abdominal region of all three corixids differs 
from that of typical Hydrocorisae in the large size of the meta- 
thoracic epimeral lobe and in the location of the first abdominal 
spiracle in the thoracico-abdominal membrane rather than in a 
recessed part of the epimeron. The three insects differ, however, 
in the shape of the metathoracic epimeral lobe (Figs. 22-24, EML), 
in the length of its dorsal opening, and in the way in which the first 
abdominal spiracular chamber is formed. In the latter two features 
Micronecta bears more resemblance to Hesperocorixa than to 
