34 ON THE STUDY OF ZOOGEOGRAPHICAL REGIONS, 



areas has clearly been brought about by the destruction of the 

 group in the dry area of country along and north of the Great 

 Bight — the Desert Barrier between East and West Australia. 

 The species of Synthemina found in Western Australia are all 

 specifically distinct from those in the East, except *S'. macrostigma, 

 which is only differentiated into the two closely allied subspecific 

 forms occidentalis and orientalis. This species also occurs, some- 

 what remarkably, in Fiji. 



The primary zoocentre of this contour is along the highlands 

 of South-eastern Australia, while a secondary zoocentre is de- 

 veloped around Cape Leeuwin. 



In many genera of animals not so dependent on the rainfall as 

 are the Odonata, this same form of contour is exhibited, but the 

 lower contour-lines of the eastern portion will lie veiy much 

 farther inland to the west, and in many cases one or more species 

 may occur across the Desert Barrier, thus linking up the two 

 portions of the contour into one complete whole. 



Other genera of Odonata exhibitins^ this contour are : — Austro- 

 gomphus, Austroceschna, Bemicor^dulia (in which the western 

 species also occur in the east, and may be linked up with them 

 when sufficient records are available). 



To a contour of this type I propose to give the name Holono- 

 tian, further distinguishing the two portions as the Eonotian on 

 the east, and the Hesperonotian on the west. The genus 

 Diphlehia exhibits an Eonotian contour only, being completely 

 absent from the South- West. Many genera in other groups of 

 animals can be shown to exhibit Eonotian contours; but, so far, 

 the only purely Hesperonotian contours known are exhibited by 

 certain genera of plants peculiar to the South- West. 



The commonest form of Holonotian contour is one in which 

 the primary zoocentre tends to be located most strongly in the 

 south-east of the continent, though it may run northwards for a 

 considerable distance as a narrow zoocentric axis. Sometimes 

 two distinct zoocentres may occur, one in the south-east, and one 

 near the border-line between New South Wales and Queensland. 

 In nearly all those cases where the zoocentre tends to be in the 

 south-east, one or more of the contour-lines will extend over 



