NO. 1389. DRAGONFLIES OF nUBMA ANT) SIAM— WILLIAMSON. 175 



The dense chalky white pruinescence of the under surface of the 

 tibia of adult males has evidently to do with sex attraction. Laidlaw " 

 records the following note ior fenestreUa: 



Dances in the air before the female, displaying wliite surface of tibise. 



In the North American Calopteryx niacuJcUa there is a definite ven- 

 tral apical abdominal spot which is shining white in living, fully adult 

 males. This area is displayed b}^ a male at rest by carving the abdo- 

 men so that the apex is brought upward and forward, the hind wings 

 meanwhile being fluttered rapidly while the front wings are held 

 motionless. The pruinose white spot thus turned dorsally becomes 

 conspicuous, especially as held between the brilliant black fluttering 

 wings. The extent of pruinescence is often a matter of age, old males 

 of some species being almost entirelj' pruinose, but the first appear- 

 ance of this is usually on the dorsum of the thorax and the dorsum of 

 the last abdominal segments, and in many species these areas alone 

 become pruinose. In the Agrionince^ where pruinescence is rarer than 

 in the subfamily under consideration, these parts, i. e., dorsum of 

 thorax and last abdominal segments, are in the males usually the most 

 conspicuously colored portions of the insects, while the abdomen of 

 the females of the same species may not be strikingly colored. In 

 species^ of EnaUa<jnia^ for example, the thoracic markings are very 

 similar in the two sexes, while the abdomen is conspicuously difl'erent. 

 It may l)e noted that the male of these species captures the female hy 

 seizing her thorax with his legs, and so holds hei' till he has fixed his 

 abdominal appendages on her ])rothorax. The male of Ar<jla jnitr/da 

 soon after emergence has the dorsum of the abdomen black. Its con- 

 geners in Indiana have th(> apical segments brightly colored, and when 

 putrida reaches sexual maturity the apical segments have become 

 pruinose. The prothorax of many of these species is ])rightly colored; 

 and the second abd(Mninal segment of the male, which bears the acces- 

 sor}^ genitalia, has a striking and conspicuous color pattern, serving 

 possibly as a guide to the female in ])ringing her vulva in contact with 

 the male genitalia. The auricles of the second a])dominal segment of 

 males in other subfamilies may serve a similar purpose. In some of 

 the Calopterygidw the basal a])dominal segments early assume a decided 

 pruinescence. The pruinose spot on the vertex of the adult male of 

 Cdniacohasis inodesta is conspicuous, and an exactly similar s])ot 

 appears in other species when the pruinescence has come to largely 

 occupy the entire body. In the Lihellullnce the male and female of 

 many species are nearly identical in color at the time of emergence, 

 while with age the male becomes largely or entirely pale bluish or 

 white pruinose, thus distinguishing the two sexes at the time of their 

 maturity. 



« Fasciculi Malay enses. p. 169. 



