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ON DIMORPHISM IN THE FEMALES OF 

 AUSTRALIAN AGRIONID^. 



By R. J. TiLLYARD, M.A., F.E.S. 



In the Proceedings of this Society for 1905 (p.302) I described 

 a dimorphic form of the female of Ischnura heterosticta Burm. 

 Since that time further examples of dimorphism have come 

 to light, and the present paper is the outcome of the results of 

 my investigations in this direction. 



Of all the genera comprising the Australian Agrionidfe, there 

 are only two in which I have been able to discover the 

 phenomenon of dimorphism. These two contain the smallest and 

 weakest species of the dragonflies known in Australia, a point 

 which serves to strengthen the contention that the existence of 

 dimorphic females is in some manner or other connected with the 

 preservation of the species. The two genera in question are 

 Ischnura and Agriocnemis. Of the former, three species (/. hetero- 

 sticta Burm., /. delicata Selys, /. senegalensis Rambur) are 

 known to inhabit Australia. The case of /. heterosticta has been 

 already dealt with. /. seiiegalensis I have never yet taken, but 

 its similarity to /. heterosticta leads me to believe that in any 



