ARTHUR DEWITT WHEDON 381 



ZYGOPTERA: 



Agrioninac: (Uilopteryx nmcidoUi Beauvois and Hetaerina 



americana Fabiicius. 

 Lestinae: Lestes imguiculatiis Hagen, L. rectangularis Say 



and others. 

 Coenagrioninae: Enallogma sj). and Ischtniw posita Hagen. 



ANISOPTERA: 



Gomphinae: Hcujenius brevistylus Setys, Gomphus amuicola 

 Walsh, G. fraterjius Say and G. exilis Selys. 



Aeshninae: Anax Junius 'Drury and Aeshnn umbrosa Walker. 



LibeUuHnae: Lihellula pulcheUa Drury, Plathemis lydia 

 Drury, Erythemis si mplici colli s Say, Perithemis domitia 

 Druiy, Sympetriwi rubicundidiu)i Say, S. semicinctum Say 

 and Tramea Carolina Linnaeus. 



EXTERNAL AXATOMY 



Both comparative morphology and paleontology agree in 

 support of the view that the Agrioninae are the most primitive 

 of living Odonata. Garman (1917) has recently summed up the 

 l)oints of importance in such phylogenctic study: they total 

 thi)ty-fivc. Of this number the Agrioninae are generalized in 

 twenty-six, the Coenagrioninae in twentj^-four, the Aeshninae in 

 ten, the Gomphinae in nine, and the Libellulinac in but five. It 

 is unnecessary' to review the evidence here. Reversing our view, 

 the Agrioninae are specialized in but nine points as against thirty 

 points in the LibeUuHnae. Personal judgment may vary on 

 certain points but there can scarcely be a doubt regarding a 

 decision where corroborative evidence is so great, and we are per- 

 fectly safe in assuming the characters of the Agrionid abdomen 

 to be most primitive. It is here, in both larva and adult, tul)ular, 

 slender, of nearly equal diameter throughout and several times as 

 long as the thorax. In the highei' groups it is modified in (1) 

 size and (2) in shape. 



Modifications in Size 



A table comparing the dimensions of the abdomen in a selected 

 list of the commoner species representative of the subfamilies of 

 North American dragonflies is given below. A glance at the 

 column of abvlominal lengths for the adults will immediately 



TRANS. AM. ENT. SOC, XLIV. 



