252 



COLORATION 



[OH. 



D. The Head Pattern (fig. 116). 



We shall only mention here two striking formations which 

 illustrate the effect of the marginal and 

 central type of pattern, respectively, on 

 the head. 



1. The Post-ocular Spots of Agrio- 

 nidae. The formation of these by stages 

 from an original marginal epicranial 

 pattern is illustrated in fig. 116 A. 



2. The T-mark on the Frons in 

 Aeschninae and Libellulidae. The form- 

 ation of this mark by stages from an 

 original central frontal pattern, and its 

 subsequent reduction to a "clear" 

 front (usually yellow), is illustrated in 

 fig. 116 B. The jewelled frons appears 

 to have been produced by an exactly 

 opposite process, i.e. extension of the 

 ground-colour, instead of reduction. 



Indications of the original marginal 

 or central type may also be found by 

 studying the clypeus and labrum. 



Fig. 116. Colour-patterns of 

 the head. A. Four stages 

 in the development of the 

 brilliant postocular spots of 

 Agrioninae from an original 

 marginal type. B. Four 

 stages in the development 

 of the T-mark and of the 

 "clear" frons from an origi- 

 nal central type. Original. 



We can profitably conclude our account of the Body-Coloration 

 of Odonata by appending a short table of the principal types of 

 colour-pattern. 



MARGINAL TYPES 



Type 



I Heliochromes 



****3SZ 



Tricolorous (Heliochromes) 

 Metallic Unicolorous 



Group 



Petalurinae 



Agrionidae 



Gomphinae, Petalurinae 



Agrionidae, some Lestidae and Calopterygidae 



Some Agrionidae 



Calopterygidae, Lestidae 



CENTRAL TYPES 



( Hylochromes 



,n . i Aphantochromes 

 ventraH T- i TT * i 



Bicolorous Heliochromes 



I Unicolorous Heliochromes 

 Annulo-central (Hylochromes) 



Metallic Unicolorous 



Aeschninae, Synthemini, Macromiini 



Some Brachytronini, Aeschna, Gynacantha 



Libellulinae, Eucorduliini 



Libellulinae 



Tetrathemini, Macromiini, Cordulegastrinae, 



Cordulephyini 

 Eucorduliini, a few Libettulinae 



