1913] Wing Veins of Membracidce 85 



atrophied. In the Coreid^e-" Ri is wanting. The weakness of 

 the vein has been remarked in the Aphididae-^ and it is entirel}^ 

 lacking in the PsylHdae-- and in the Aleurodidas^^. In fact, 

 Comstock and Needham state-'* that the complete absence of 

 the vein Ri is one of the most characteristic features in the 

 venation of the wings of the Hemiptera. 



It is of some phylogenetic interest, then, to note that in the 

 Membracidae, while the vein is abnormal, it is not completely 

 absent, and in this respect the membracid wings may be con- 

 sidered the most generalized of any of the families of Homoptera, 

 at least those of which the homologies of wing-veins have been 

 determined. 



Most of the genera of the Membracidae show the position 

 of Ri as described. In many it has been impossible to find the 

 trachea, although the vein is present and constant. Since, 

 however, the history of the vein is evidently traceable to the 

 trachea representing Ri, it seems necessary to call this vein 

 Ri whenever it appears. 



In a few genera, namely, Acutalis, Tylopelta, Enchenopa, 

 Campylenchia, Platycentrus, and Centruchoides , the vein comes 

 off in its normal position. In the nymphal wings of Enchenopa 

 binotata, for example (Fig. 12), the trachea is found in its 

 natural place. These genera are, of course, still more gener- 

 alized with regard to this special point, but are not so typical 

 of the family. 



The course of the rest of radius is evident from the trachea- 

 tion. At its base it often anastomoses for some distance with 

 media before these two principal veins separate for their 

 respective courses through the wing. In Ceresa, Stictocephala, 

 etc., this coalescence must be fairly constant, since it has been 

 made a basis for classification25. R2+3 usually extends undi- 

 vided to the tip of the wing. It is generally connected with 

 R4+5 by a cross-vein. R4+5 is represented as one vein and 

 coalesces with the anterior branch of media (M1+2) for a more 

 or less extended part of its course. The amount of coalescence 



20. Wings of Insects, p. 252. 



21. Annals of the Entomological Society of America, 1909, Vol. II, p. 111. 



22. Annals Ent. Soc. of Amer., 1909, Vol. II, p. 119. 



23. Annals Ent. Soc. of Amer., 1909, Vol. II, p. 122. 



24. Wings of Insects, p. 245. 



25. Biologia Central! Americana, Insecta; Rhynchota, Homoptera, Part II, 

 p. 87. 



