242 Annals Entomological Society of America [\'ol. XI. 



Notum. The metanotuin varies in the Heteroptera from a 

 size nearly equal to that of the mesonotum to a small section 

 almost entirely concealed under the scutellum of the meso- 

 thorax. The pretergite (prt), if present, is indistinguishably 

 fused with the posterior phragma of the mesothorax. A narrow 

 prescutum (psc) is often visible, but it is closely united with the 

 mesothoracic postscutellum (psl2) often adhering to it when 

 the mesothorax and metathorax are pulled apart. Prescutum 

 (psc), scutum (sc) and scutellum (si) are sometimes, as in the 

 Corixidas (Figure 19), Notonectidae (Figure 16), Nabidas (Figure 

 24), Cimicidse and Berytidae (Figure 22), inseparably fused 

 together. In some cases, on the other hand, one, two, or all 

 three of these sclerites are definitely marked off by sutures. 

 The postscutellum (psl) is found in all gradations, from a brief, 

 partially hidden plate, as in Belostoma (Figure 20), to a large, 

 extensive sclerite, as in the Berytidae (Figure 22). 



In the Gerridae (Figure 21) the homologies of the parts of 

 the metanotum are not easily determined. There is apparently 

 a short plate composing the scutoscutellum (ssls), rather long 

 mesally and coming forward to a point on either side to reach 

 the narrow wing bases, which are set somewhat forward. 

 Behind this is the rather extensive postscutellum (psU), likewise 

 extending forward in a point on each side, and very broadly 

 joined to the epimeron (ems). 



In the Coreidae (Figure 23) and similar forms a narrow, 

 raised portion (cca), the cenchrus of Hemipterologists, extends 

 along the upper margin of the epimeron (ems) where the pos- 

 talare (poas) joins it. This is possibly homologous with the 

 parapleuron of Coleopterologists. 



Pleuron. The pleuron of the metathorax is in general similar 

 to that of the preceding segment. The distorted condition men- 

 tioned above is most noticeable in the Corixidae (Figure 19), 

 Notonectidae (Figure 16) and Belostomatidse (Figure 20). In 

 Corixa (Figure 19) the coxa (cxs) is very large and its base is 

 covered by flaps of both episternum (ess) and epimeron (ems). 

 The pleural suture (ps) is nearly horizontal and lies very near 

 the upper margin of the pleuron. The epimeron (ems) is thus 

 very narrow. Only in Belostoma (Figure 20) is the metathoracic 

 episternum divided into anepisternum (aes) and katepisternum 

 (kes). In Notonecta (Figure 16) and in Belostoma (Figure; 20) 

 the epimeron (em) does not overlap the coxa, but the episternum 



