BY n. J. TILLYARD. 423 



The above subdivision of the genus Lesfes emphasises certain 

 points of phylogenetic interest, viz.: — 



1. AusfroleMes must, be regarded as a more advanced type tlian 

 Lei<t.es(s.siY.), the reasons for this being : — 



a. Originally, all Odonata rested with outspread wings, and 

 this custom prevailed also amongst tlie ancestors of our present- 

 day Zyyoptpra. Gradually, however, as the astlienogenetic 

 development of tliis group proceeded, it became more and more 

 advantageous to them to be able to hide away without attracting 

 notice; so that we find nearly all present-day Zygoptera adopting 

 this plan. The chief exceptions seem to be the rock-dwellers on 

 fast mountain-streams (e.f/., Dlplilebia, Argiolfstes), which, having 

 no particular hiding-places, have continued the habit of resting 

 with outspread wings, and have developed consideral)le alertness 

 of movement (on the lines of the Gompkiufv,) from the position of 

 rest. The fact that Leste^ifi.^tv.) has not developed the habit of 

 resting with folded wings, in spite (jf its obvious advantage to 

 them, seems to be a strong argument for my statement. 



h. The sectors of the arculus arise lower down in Austrolestes 

 than in Lestes{&.Htv.). Tliis is a sign of greater specialisation. 



c. Although in liotli Lextf.siii.iitv.) und Austrolestes, iha inferior 

 sector of the triangle proceeds backwards basally only as far as 

 the basal postcostal nervulc(compare Fseudagrioa), yet a careful 

 examination, under a liigh power, shows nearly always less com- 

 pleteness in this reduction in Lestes{ii,.iitr.) than in Austrolestes 

 {i.e., the sector fuses with the wing-margin just a little beyond 

 the cross-vein towards the wing-base). 



d. Austrolestes is more astlienogenetic than Li'stes(^.'ati\) in the 

 reduction in width and in area of its wings, compared to the size 

 of the insect itself. 



2. The greater astlienogenetic specialisation of Austrolestes has 

 enabled it to take a position in the Australian Odmtafr fauna 

 more analogous to that of Agrioii in Palaearctic regions than to 

 that of //'^.s'^e.s(s.str.). Tt is prohablv as a conseijuence of this that 

 the metallic green colouration of the older Lesf,es{H.iiii\) has given 

 place in Aastrolestes to a more distinctly bicolorous pattern of 



