776 STUDY OF THE ODONATA OF TASMANIA, 



species, confined to the southern parts of Australia. There seems 

 very little doubt that it, too, must be a remnant of some ancient 

 Libelluline group now almost extinct. 



Not less extraordinary than the case of Diplacodes, is the failure 

 of the strong-flying and very abundant still-water species, Anax 

 papuensis, to appear in Tasmania. This species may often be 

 seen flying in the streets of the city of Melbourne, and it seems that 

 it can only be a matter of time before it must establish itself in 

 Launceston, considering the frequent communication between the 

 two ports. The fact that it has failed, so far, to negotiate 200 

 miles of sea, with islands en route, shows how very seldom Odonata 

 are dispersed across even narrow straits. Apart from a strong 

 tendency to migrate, exhibited by a few Libellulid genera, there 

 seems no reason to suppose that dragonflies are ever carried far 

 from their breeding grounds. When storm or wind arises, they 

 immediately seek shelter; indeed, they do so usually some time 

 before the disturbance breaks upon them. 



Argiolestes icteromelas and Hemicordnlia australice are both 

 very abundant in Southern Victoria; but, as they breed in running 

 water, their inability to cross over is explainable on the hypothesis 

 already offered. 



The case of Hemicordnlia tau has some special features. This 

 species is exceedingly abundant in Victoria, but quite rare in Tas- 

 mania. It is only in occupation of occasional pools and water- 

 holes, and, in particular, of artificially constructed dams. It is the 

 only southern Australian species which has developed a migratory 

 tendency. Particularly in the autumn, when a second brood 

 appears, it is recorded at intervals of a few years apart, as appear- 

 ing in thousands over large areas, and travelling for many miles. 

 I am strongly of opinion that Hemicordnlia tau is the most recent 

 addition to the donate fauna of Tasmania, and that the scanty 

 colonisation of the island, by this species, has been brought about 

 by the successful passage of Bass Straits by portion of one of these 

 migratory swarms, probably within the last few years. The fact 

 that it has not yet colonised the large swamps and lagoons, is a 

 strong argument for this view. 



