BY R. J. TILLYARD. 451 



important respects, notably in the approximation of the triangle 

 to the arculus, and in the remarkable colour-scheme of the wings, 

 that it seems highly improbable that they ever existed in any other 

 parts of the world. All the species are evidently closely allied, 

 so that one is bound to postulate for them, not so ver}^ long ago 

 in geological time, a common ancestor of a type not far removed 

 from Archipetalia. The only satisfactory explanation of this 

 problem, as it seems to me, is to be found in the Antarctic 

 Theory, as elaborated by Hedley;* indeed, the group offers almost 

 as fine a vindication of the theory as one could have hoped to 

 find at the present day. Assuming that the connnon ancestor of 

 the group existed on the Antarctic Continent at a time when 

 the climate was sub-alpine, then, with the lowering of the tem- 

 perature to the minimum at which Odonate life was possible, 

 either the group would have become extinct, or it would have 

 been saved by migration along the only paths open to it. Ac- 

 cording to Hedley, this Antarctic Continent was connected at 

 different times with {a) Tasmania and South-Eastern Australia, 

 (6) New Zealand, and (c) Patagonia and S. Chili, by means of 

 long, narrow strips of land. The group must, therefore, have 

 travelled outwards from the place of origin along these three 

 land-connections, and its descendants must be looked for in the 

 higher altitudes of these three regions. The three Chilian genera 

 have been known for some time, but the number of specimens 

 obtained is still very small. The Blue Mountain species, Austro- 

 petalia patricia Tillyard, was first discovered in 1 903, but it was 

 not until nine years later that another specimen was obtained, 

 though it was carefully searched for in the interval. In dealing 

 with this species in a previous paper,! before tlie discovery of 

 the Tasmanian form, I discussed the possibility of an Antarctic 

 origin for the group, in the following words: — "This theory would 

 undoubtedly be strengthened by the discovery of a Tasmanian 



" "The Palaeographical Relations of Antarctica," by C. Hedley, F.L.S., 

 Proc. Linn. Soc. London, Session 124, 1911-12, pp,80-90. 



t " Life-Histories and Descriptions of Australian jEschnind'." Jomni, 

 Linn. Soc. London, Zoology, xxxiii., 1916, p.21. 



