BY R. J. TILLYAHD. 385 



trophya, Idionyx, Neophya: and pi'obably also Idomacromia, 

 about which our knowledge is far too little to make a definite 

 position possible. 



Tlie relation of the four main groups of the Corduliitice may 

 now be illustrated as follows : — 



jj I , Eucordulina 



0) < 

 > O. I si 



5^ ( Idocoriluliiia 

 p J 



^ (^ Syntliemiiia 

 Macroiniiia ■ 



C8 - 



I g 



I— I aj 



Returning now to the question of Ilespe.rocordulia and Lathro- 

 corduJia, it seems, at first sight, that these two genera are very 

 closely allied. This may be actually the case, or it may be the 

 result of convergence; the point can probably n(jt be definitely 

 settled until the life-histories are known. The important thing is 

 to recognise that, in the natural development of coordinate groups, 

 the Jii'st divergence or dichotomy must have yielded two closely 

 allied forms; and that it has been the gi-adual widening of the 

 gap, by development along the two new lines, that provides us 

 with the main characters for our group-classification. Now in 

 the imago of Hesperocordulia, we find the beginning of the 

 tendency towards an elongated anal loop (the same is shewn 

 in Oxyyastra); we have a hind wing-triangle practically quite 

 recessed, and we have also a robust development of head 

 and thorax, and very long legs. Place the insect side by side 

 with Lathroccn-dulia, and the remarkable difference in the lensfth 

 of the legs is at once seen. Comparing the two anal loops, the 

 shortness of the loop in Lathrocordulia is intensified by its lack 

 of a definite longitudinal bisector; in Hesperocordulia the bisector 

 is fairly distinct, and the apical end of the loop is closed by a 

 straight vein. Lathrocordidm is clearly very close to tiyncor- 

 dulia, and should be placed in the Idocordulina, J/esperocor- 

 didia, on the other hand, in spite of its thin abdomen, is certainly 

 on the road to full F ncordidiria-dey elopment. 



The following table shews, at a glance, the more important 

 generic characters of Hesperocordulia, and the five Austi-alian 

 genera comprised in the group Idocordulina :— 



