384 DIMORPHISM IN FEMALES OF AUSTRALIAN AGRIONIDiE, 



Genus Ischnura. 



/. heterosticta Burm., possesses a well-developed dimorphic 

 female, a complete mimic of the male. This form occurs in all 

 localities where the ordinary form is found and is fairly common, 

 comprising from 30-40% of all the females taken. 



/. delicata Selys. — The dimorphic female, which is a well- 

 developed male-uiimicking form, is exceedingly rare, only 

 occurring in a few localities in South- Western Australia. I took 

 it first at Bridgetown on the Blackwood River. The species is 

 by no means common here; out of a dozen females taken two 

 were dimorpbs. At Wilgarrup, some fifteen miles from Bridge- 

 town, and in the Warren Kiver district, this species was in great 

 abundance, the males flying up in clouds from the rich grass 

 that fringes the continually running and often boggy creeks. 

 Here I was able to capture a great many females, with the result 

 that about 10% were dimorphs. Three of these had the tips of 

 the abdomen smeared with brown mud, indicating that they had 

 already been ovipositing along the margins of the creek. 



The following is a comparative description of the two forms: — 

 Ischnura delicata Selys 9. 



Total length 24-25 mm. ; abdomen 19-20 mm. ; forewing 

 14-15 mm.; hindwing 13-14 mm. 



Wings: Neuration very slender, pterostigma lozenge- 

 shaped, 0'6mm., very pale dirty brown. Nodal Indicator 2 6-8 

 Head: Eyes black above, yellowish-green in front and \2 5-6 

 below; a brilliant pale blue spot on the orbit behind each eye. 

 Upicranium black, with a transverse yellowish-green band in 

 front next the clypeus, in a line with the green portion of the 

 eyes. Clypeus black ; labrum yellowish ; labium pale dirty 

 greyish-white, or straw-coloured. Thorax: Prothorax black 

 above, yellowish on sides. Meso- and metathorax black above, 

 with a pair of narrow olive-green or yellowish-green bands, sides 

 greenish. Leys pale yellow or straw-coloured, femora marked 

 with a black line for half their length from elbow. 



