H)1S1 



Thoracic Sclerites of Ileniiptera 



245 



Neuropteroid mesothoracic episternum. The general plan of 

 the Cicadid thorax is followed in the Aphididse, Membracidae, 

 Psyllidae, Cercopidae and Fulgoridas. Of these, however, all but 

 the Aphidid^e and perhaps the Psyllidae present striking mod- 

 ifications, such as the extreme specialization of the Membracid 

 prothorax, and the remarkable fusion of the coxae and the meta- 

 thoracic pleura of the Fulgoridas, the latter of which seems to 

 have originated in a similar condition (less marked) in the 

 Cercopidae. The Membracidae and Fulgoridae, therefore, seem 

 to be nearly related w4th respect to the thorax. The thorax of 

 the Aleyrodidae, being extremely small and lacking in pigment, 

 cannot be carefully compared with that of the other families. 

 Its large metathoracic coxa, immovably fused with the pleuron, 

 may connect it with the Fulgoridae. The following diagram 

 illustrates to some extent the relationships shown by the 

 thorax, without regard to primitiveness. 



'Xeuropteroid thorax. 



Cicadida- 



Jassida? 



Aphididce 



Psyllida- 



McmTiracida' Specialized ])rothorax. 



Cercopidae 



Similar thoracic 

 plan with but few 

 modifications. 



Simila,r 

 general 

 thoracic 

 plan. 



Fulgorida" {-Peculiar fu.sion of metathoracic .sclerites and 



I coxas _ 



Aleyrodidit J 



In the Heteroptera the thoracic structures of all the families 

 are similar in their general composition. The relation of the 

 coxae to the pleural plates differs to some extent and may in a 

 way serve to indicate some of the more general relationships. 

 The Notonectidae, Corixidae, Belostomatidae and Nepidae are 

 apparently related, both because of the distorted condition of 

 the thorax, mentioned above, and from the large size of the 

 metacoxa, which is overlapped more or less by the pleural 

 plates. The remaining families studied in this paper seem very 

 similar in the construction of the thorax. In the Capsidae, 

 Nabidae and Cimicidae the mesothoracic and metathoracic coxae 

 are entirely exposed, or nearly so, not being overlapped by the 

 pleural plates. The relation of the Cimicidae to the other two is 



