26 connecticut geol. and nat. hist. survey [buu. 



Table of Comparison of Venation al Systems in the Orders 



Protodonata and Odonata 



(Convex veins marked +, concave veins — ) 



Name of vein 

 Costa (+) 

 Subcosta ( — ) 

 Radius (+) 



Main stem ( + ) 



Radial sector ( — ) 



Media ( — ) 



Anterior branch (-)-) 

 Posterior branch ( — ) 



Cubitus ( — ) 

 Anterior branch ( + ) 

 PosterixDr branch ( — ) 



Analis ( — ) 



Anterior branch ( + ) 

 Posterior branch ( — ) 



* Regarded as absent except in the Protagriidae, a group of primitive Odonata from 

 which the Agrionidae were probably derived. 



The relative position of the different families in our scheme of 

 classification has been outlined in the Zygoptera of Illinois, p. 463, 

 191 7. It will be seen that the Agrionidae and Coenagrionidae are 

 very close in point of specialization. Since this work was pub- 

 lished it has become apparent from the work of Kennedy and 

 Tillyard, who have considered the relationships from morphologi- 

 cal and paleontological evidence that the original position of the 

 Agrionidae as the most generalized and hence at the bottom of 

 the list, is open to question. The structure of the genitalia and 

 the discovery of Kennedya in the Permian of Kansas casts con- 

 siderable doubt on the hitherto-accepted interpretation. There still 

 remain, however, points which need clearing up. These are found 

 in the important retention of the interpleural suture in the adult 

 Agrionidae and the cleft and primitive condition of the labium 

 of the Agrionid nymph. These facts, together with the fact that 

 so few fossils are known from the Permian, would indicate that 

 any position taken in regard to the relative generalization of these 

 two families may be easily overthrown by future discoveries in 

 paleontology or extensive work upon the morphology. Possibly 

 the origin of both Agrionidae and Coenagrionidae may be carried 



