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ON" DIMORPHISM IN THE FEMALE OF ISCHXURA 

 HETEROSTICTA, BURM. 



By R. J. TiLLYARD, B.A. 



The pretty little dragonfly, Iscluiura heterosticta, belongs to the 

 family Agrionidce, of which there are about thirty known species 

 in Australia. Of these, six belong to the genus Ischnura. They 

 are remarkable for their brilliant colours and small size. Very 

 little is known of their habits, owing to the difficulty of collect- 

 ing them. /. heterosticta is our largest species; the male, being 

 very conspicuous, is often collected where the duller female is 

 overlooked. It is common in the neighbourhood of Sydney, and 

 extends southwards across Victoria to South Australia, while 

 northwards it is plentiful as far as Brisbane, and probably has 

 an extended range further up the coast. It flies from October 

 to March. 



While collecting at Cook's River in February last, I found a 

 remarkable new female form of this species. An hour's hunting 

 had yielded about a dozen beautifully coloured insects which 

 appeared to be males, with half a dozen females of the ordinary 

 dull blackish type. On examination, however, it was found that^ 

 with the exception of three, all the supposed males were in 

 reality females; yet so closely did they resemble the male in form 

 and colouring that the fact might easily have been overlooked. 



The male differs from the typical female in having the sides of 

 the thorax, the first two and last two segments of the abdomen 

 brilliantly coloured with rich blue. The female has no blue 

 markings, and the abdomen is of a uniform dull fuscous, approach- 

 ing black. The abdomen of the male is very slender, with the 



