246 



Annals Entomological Society of America [VoX. XI, 



somewhat problematic, the flattening of the thorax and con- 

 sequent contraction of the thoracic plates giving these insects a 

 unique place in the order. The Reduviidae and Phymatidas, 

 unlike any others of the families studied, have a true coxal cleft 

 in the metathorax, homologous with that in the mesothorax. 

 The Pentatomidae, Scutelleridse and Corymelaenidee may be 

 grouped on account of the extremely developed mesothoracic 

 scutellum, which projects far over the abdomen. The chief 

 reasons for uniting the Berytida3 and Gerridae in the diagram 

 below are the horizontal lengthening of the mesopleura. and the 

 metathoracic scutellum, which in both joins broadly with the 

 epimeron ventrad. The Emesidae also resemble these two fam- 

 ilies, though their relation to them may be questioned. The 

 following diagram is an attempt at grouping those Heterop- 

 terous families, which appear from their thoracic sclerites to be 

 related. 



Notonectidse. . . 



Corixidae. 



Belostomatidas . 



Nepidae 



Capsidae. 



.1 



Large metathoracic coxae, overlapped by episterna; meso- 

 thoracic and metathoracic pleura distorted. 



Nabidas i-Coxae of both mesothorax and metathoraxl 1 



I entirely exposed, or nearly so j 



(Cimicidae) J 



Reduviidae ] True coxal cleft in metathorax; meso- 



\ thoracic sternum and pleuron separated 

 Phymatidae j by a suture 



Coreidae 



Lygaeidas 



Tingitidae 



Pentatomidfe 1 



Scutelleridas [Mesothoracic scutellum prolonged over abdomen. 



Corymelaenidas... .J 

 Berytidae 



Similarity 

 in general 

 structure; 

 pleura of 

 [■meso- and 

 metathorax 

 usually 

 rectangular 

 in sliajie. 



Gerridae. . 

 Emesidae. 



Pleura of mesothorax lengthened hori-) 

 zontally; metathoracic epimeron broadly K 

 joined to postscutellum .J 



