DRAGONFLIES OF OHIO. 



primative stock ; to those orders having representa- 

 tives at lower geological horizons than Metabola. 

 They present, however, some contrasts and exceptions 

 to those of related orders. In these the head thorax 

 and abdomen are sharply separated as in Metabola. 

 They are active, powerful and boldly predaceous. 

 Their nymphs, as well as the adults, exhibit the malig- 

 nant side of life that lived and sported about the 

 marshes of the remote Tertiary Period. 



LESSER GROUPS OF THE ORDER. 



The Order Odonata is divided into two sub-orders : 

 I. Zygoptera in which both pairs of wings are 

 similar and which in repose are held vertically; the 

 males have two inferior abdominal appendages and the 

 nymphs have three caudal gill-plates ; and II. Anisop- 

 tera in which the two pairs of wings are dissimilar, in 

 repose they are held horizontally; the males have one 

 terminal inferior abdominal appendage, and the 

 nymphs have no terminal gill-plates. 



Our representatives of the Order may be arranged 

 in the following lesser groups : 



Order ODONATA. 



I. Sub-order Zygoptera. 



1. Family Agrionid^e. 



(1) Sub-family Calopteryginse. 



(2) Sub-family Agrioninae. 



II. Sub-order Anisoptera. 



2. Family ^EscHNiDiE. 



( 3 ) Sub-family Gomphinse. 



(4) Sub-family Cord uligasterinse. 



(5) Sub-family iEschninae. 



