12 E. B. Williamson 



Gynacantha inembraitalis Karsch. 



Gyuacantha mcxicana Selys. 



Gynacantha nervosa Rambur. 



Gynacantha robusta Kolbe. See text under G. bifida. 



Gynacantha (Aeshna) subviridis Selys. See text under G. aurictilaris. 



Gynacantha tenuis Martin. 



Gynacantha tibiata Karsch. 



Species are arranged in the text in the same order as in the tabulation of vona- 

 tional characters as follows : T. septima, dilzleri, caribbca, triUda, satynis, G. laticeps, 

 chelifcra (and aratrix). adela, conver^ens. tenuis, caudata. tibiata, jessei. aitricularis. 

 klagesi, ereagris, nic.vicana, nervosa, bifida, croccipennis, litoralis, intcrioris, gracilis, 

 and niembranalis. 



Key to American Species of Triacanthagyna and Gynacantha 



I. Two rows of cells between Mi and M2 beginning under the stigma; fork of Ks 

 near the proximal end of the stigma in the front wing (except in trifida) and 

 more basal in the hind wing than in the front wing. Third joint of penis in 

 ventral view elliptical, without membranous margins, from slightly shorter than 

 to less than half as long as the second joint, and only slightly wider; ligula rela- 

 tively long and narrow, in ventral view sul)equal in width ; superior appendage 

 with a short narrowed base, apically blade-like, with parallel or subparailel mar- 

 gins to near the minutely toothed apex, the blade without carinae or processes ; 

 posterior part of hamular process relatively low and therefore appearing more 

 nearly horizontal, with no deep sulcus entirely across the process dividing it from 

 the anterior part, which is relatively narrow. Ventral process on abdominal seg- 

 ment 10 of female three-pronged. So far as observed crepuscular, flying in the 

 evening and rarely in the morning; flight very erratic. Triacanthagyna. 2. 



I.' Two rows of cells between Mi and M2 beginning at or proximal to the stigma 

 in the hind wing and usually in the front wing; fork of Rs distinctly basal to 

 the stigma in the front wing and more basal in the hind wing (except in ara- 

 trix). Third joint of penis in ventral view roughly triangular with a large 

 expanded membranous basal margin on each side, equal to or 

 slightly exceeding the second joint in length, and nearly or quite twice as wide; 

 ligula relatively shorter, wider caudad, not subequal in width in ventral view; 

 appendages variously shaped ; posterior part of hamular process high and 

 vertical or subvertical, sharply divided by a deep sulcus, which extends across 

 the process, from the anterior part which is broad and thin. Ventral process 

 on abdominal segment 10 of female two-pronged. Habits varied, when crepus- 

 cular, flight less erratic and often in regular beats at a uniform height. 



Gynacantha. 6. 



2 (i). Legs entirely pale; thorax without definite dark markings; abdomen pale; 



anterior edge of frons seen from above convex. Male with abdomen not con- 

 stricted at segment 3 ; the opposing hairs on the blades of the superior appendages 

 reduced in lengtli from the base to the middle of the blade, the apical half with 

 only ordinary short hairs septima. 



2! Legs more or less dark, in tenerals the legs are pale but the apices of the 

 femora and bases of the tarsi dark to black; thorax with definite dark markings; 

 abdomen dark ; anterior edge of frons seen from above more or less angled. 

 Male with abdomen constricted at segment 3 ; the opposing hairs on the blades 

 of the superior appendages about equally long and numerous the entire length 

 of the blade irifida group. 3. 



3 (2'). Anterior row of cells in anal loop usually consisting of two cells; second 



and third femora similar in color. Hamular process relatively small and short, 

 less than .4 in length, equal to much less than one-third the distance from its 



