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PROCEEDINGS OF THE NATIONAL MUSEUM. 



cross vein forming the lower end of the arculus/' This is ontirel 

 absent from the fore wing of the males; it is present, however, in tb 

 hind wing of both sexes, and often also in the fore wing of the femah 

 The loss of this cross vein has resulted from a shift of other veins an 

 a consequent shift of responsibility in stress of wing stroke. Tl 

 synmietrical fork formed at the separation of veins 31^+^ and J/, (els. 

 where always unilateral unless the fork be very narrow) and the upwai 

 bend of the anal vein at its departure from the hind margin, to mefti 

 the cu])ito-anal cross vein and the very considerable progression of tit 

 arculus beyond the second antenodal, are the visible signs of the reac 

 justment which has relieved the basal side of the quadrangle of i 

 former responsibility. 



It is needless to remark after observing the form of the wings, th; 

 among the Zygoptera there are no strong flying species. Most ( 

 them fly so low over the surface of the water that their winge; 

 enemies can not safely descend to their level. The Lestina^ live ami 

 sheltering semiaquatic vegetation. Vestalinfe seem not to be desire 

 for food; their coloring may suggest that they are not good eatinj 

 The action of the wings is that of sculling solely; only the distal po 

 tion of the wing which takes the active part in insects' flight is we' 

 developed. There is no soaring basal aeroplane, as in the Anisopteri 

 to support the body passively by merely gliding upon the resistant ai 



1 ort'er below a scheme of subfamilies for the order, which seems I 

 me to be, in the light of the evidence that present knowledge of vent 

 tion affords, an approximation toward equivalent values for theft' 

 groups. The weakest distinction seems to me to be between the Co 

 dulina^ and the Libellulina?; the most doubtful association of recei 

 forms that of Cor did eg aster and Petalia together. The fossil grou]i 

 seem not onl}^ more isolated but also more strongl}^ characterize 

 structurally than the others. 



1. Gomphinx (recent and fossil). 



2. Petalurinse (recent and fossil). 



3. Stenophlehinas (fossil). 



4. Cordulegasterinie (recent and fossil). 



5. Chlorogomphinx (recent). 



6. JEschninx (recent and fossil). 



7. yEsdmidiinve (fossil). 



8. MacTomiimr, (recent). 



9. Cordulinx (recent and fossil). 



10. Libcllulinic (recent and fossil). 



11. Ileterophlebinse (fossil). 



12. Palaeophlebimx (recent). 



13. Epalhui'mx (recent and fossil). 



14. Vestalimv (recent). 



15. Thor'ma' ( recent) . 



16. Lestime (recent and fossil). 



17. Agrioninse (recent and fossil). 



Anisoptera. 



yEschnidfe. 



Lil)ellulida 



Zygoptera. 



CalopterygidsB. 



Agrionida;. 



«This arcnlus cross vein is absent in the fossil genus Tarsophlebia as already note 



