1976] 
Parsons — Morphology of Corixidae 
145 
The metathoracic spiracle (concealed in Fig. 14 A) is located 
anterior to the intersegmental boundary in all Hydrocorisae which 
have been examined thus far (Parsons 1974). It lies on the meso- 
thoracic epimeron, and usually opens onto the lateral interseg- 
mental or ventral intersegmental air space (Positions 1 and 2, 
respectively, of Parsons 1974). It is thus concealed externally 
by the lateral ridge or posterior lobe of the mesothoracic epimeron. 
In Hesperocorixa and Notonecta, however, the spiracle lies im- 
mediately adjacent to the mesothoracic scolopophorous organ, 
on the dorsal, vertical part of the epimeron, and opens directly 
onto the subalar air space (Position 3 of Parsons 1974). 
II. Diaprepocoris 
Of the three corixids examined, Diaprepocoris shows the least 
modification of the typical plan diagrammed in Fig. 14 A. The 
lateral lobe of the mesothoracic epimeron (Fig. 15, LL) is relatively 
narrow and projects laterally and somewhat dorsally, as in typical 
Hydrocorisae, rather than curving sharply dorsally, as in Micro- 
necta and Hesperocorixa (Fig. 14B). Thus the costal margin of 
the wing lies farther ventrally on the body than in the latter two 
insects. 
Posterior to the wing-anchoring knob of the mesothoracic epi- 
meron, the margin of the forewing fits into a horizontal groove 
(Fig. 15, W) on the metathoracic episternum. The homologies of 
this groove are uncertain. Unlike the wing-holding devices on the 
metathoracic episterna of Micronecta (Fig. 16, W) and Hespero- 
corixa (Fig. 17, W), it lies far ventral to, rather than at the level 
of, the metathoracic coxal process (Fig. 18, PR), and appears ex- 
ternally as a groove rather than as a ridge. In addition, it does not 
form the ventral boundary of a well-developed “air trough” such 
as that of Hesperocorixa (Fig. 17, AT). In the latter, both the epi- 
meron and the episternum of the metathorax are strongly indented 
in the region of the pleural sulcus (PL III). In Diaprepocoris, as 
in most other Hydrocorisae, only the dorsal portion of the epi- 
sternum and a small portion of the epimeron are indented in this 
region (Fig. 15). 
The boundary between the mesothorax and metathorax is 
marked dorsally by the second phragma (Fig. 18, 2PH). Ventral 
to the mesothoracic scolopophorous organ (SO II) the boundary 
bends sharply anteriorly and then curves posteromedially onto 
the ventral surface of the body. The portion of the boundary 
