244 Anna Is En torn ological Society of A m erica [\o\. XI, 



found in other forms where the pleural suture is absent, extend- 

 ing in a similar direction. 



The general shape of the metapleuron in those forms where 

 the pleural suture is absent is rectangular. In many forms the 

 upper forward margin of the metathoracic pleuron extends 

 slightly beneath, or at least anterior to the rear margin of the 

 mesothoracic pleuron. This is true of the Nabidae (Figure 24), 

 Gerridse (Figure 21) and Berytidae (Figure 22) and of other 

 forms not figured. It is particularly well shown in Gerris 

 (Figure 21), where the rear wing lies very far forward, and the 

 pleuron extends beyond it to support it. 



In one . of the elongate forms, Eniesa (Figure 14), the 

 efpimera (ems) of each side present the appearance of meeting 

 dorsally and bridging the region behind the postscutellum (psls). 

 Though this may seem an improbable conception, it may not 

 be an impossible one, since it will be recalled that in the meso- 

 thorax of Odonata the two episterna meet in front of the notum 

 in much the same fashion. 



Openings of scent glands (sg) occur in a number of families. 

 These are represented in the figure of the squash bug (Figure 

 23). The opening is located at the end of the coxal cleft (dj) in 

 the lower anterior corner of the episternum (es?) . 



Sternum. The metasternum is quite like the mesosternum 

 in the Heteroptera. It Consists of one plate (sts) usually and is 

 not often separated from the episternum. A narrow postcoxale 

 (pocs), usually concealed, passes behind the coxa (cx.3) from 

 epimeron (em.s) to sternum (sts). This postcoxale is externally 

 visible in Coriscns (Figure 24, poc;0. 



RELATIONSHIPS OF THE HEMIPTERA INDICATED BY THE 

 THORACIC SCLERITES. 



On account of the diversity in the thoracic structure of 

 Hemiptera, it is difficult to interpret the relationships of the 

 families. Aloreover, there are in the sclerites of some forms 

 modifications, the origin of which is uncertain, there being 

 apparently no intermediate or ancestral conditions leading up 

 to these modifications in the forms studied. Hence it has been 

 possible only to group together certain families whose thoracic 

 sclerites most resemble each other. 



Among the Homoptera the Cicadidse exhibit certain features 

 in common with the Jassidae, of which the most striking is the 



