xin] 



COLORATION 



257 



Colour Dimorphism (Plate III, figs. 17-24). 



Apart from what is known as sexual dimorphism in colour 

 (i.e. the male and female differing in colour) a phenomenon of 

 wide occurrence in the Odonata there is a very interesting group 

 of Agrionini in which two forms of females nearly always occur. 

 This group embraces the genera Ischnura, Ceratura, Anomalagrion, 

 Agriocnemis and Austrocnemis. In all cases, one form of female 

 is commoner than the other. The commoner form may be called 

 the "normal," the rarer one the " heteromorphic " female. Either 

 of these may be similar to the male (homochrome) or unlike it 

 (heterochrome). Where the heterochrome is normal, it is usually 

 of a dull blackish, olive, or greenish colour. Where the hetero- 

 chrome is the heteromorph, it usually assumes a rich orange 

 or red form. I offer a short table which embraces all the different 

 types known to me: 



Heteromorphic Female 

 Heterochrome (orange 

 and black) 



Heterochrome (red and 

 bronze) 



Homochrome 



Heterochrome (orange 



and black) 

 Heterochrome (orange 



and black) 



Heterochrome (orange 



and black) 

 Heterochrome (red and 



black) 



Silver 



(dull 



Heterochrome (red and 

 black) 



Species 

 Ceratura and 



many species 



of Ischnura 

 Austrocnemis 



(Plate III, figs. 



20, 21) 

 Ischnura hetero- 



sticta 

 /. ramburii, I. 



perparva 

 I. pruinescens 



(Plate III, figs. 



17-19) 

 Anomalagrion 



I. aurora 



Most species of 

 Agriocnemis 



Agr. hyacin- 

 thugi (Plate 

 III, figs. 22- 

 24) 



Agr. argentea 



Heterochrome 

 blackish) 



1 Agr. pygmaea Ramb., of which Agr. hyacinthus is probably only a subspecies, 

 has an orange female. In series of this insect from the Seychelles, Campion has 

 noted the occurrence of structural as well as colour dimorphism in the females, the 

 prothorax having its hind-margin distinctly lobed. In view, however, of the facts 

 that the form of the prothorax is closely correlated with that of the appendages 

 of the male, and that no males were taken with this supposed new form of female, 

 it seems more likely that this will really prove to be a new species. 



T. D.-F. 17 



