314 DRAGONFLIES OF NORTH AMERICA 
Enallagma is essentially a holarctic genus, with its center of distribu- 
tion in the United States. However, a number of species have been 
described from Africa and from the islands of the Pacific. The present 
account embodies all the New World species with the exception of E. 
krugit Kolbe, E. truncatum Gundlach, from Porto Rico and Cuba, and 
probably EH. simile Selys from Venezuela. 
The Known Nymphs 


Setae Gills 
Species Length* Ext} | Combt Pigmentation Described by 
Lat. | Ment 
antennatum 144+7.5 | 4-5 3 7-8 % Basal 24 & apex] Ndm. ’03, p. 257 
boreale 15+7 6 4 5-6 w+ Tracheae only Walk. 16, p. 192 
carunculatum 14+6 6 3 8-9 Bu Tracheae only Ndm. '03, p. 255 
civile 15+6 5-6 3-4 7-8 Y— | Tracheae only Ndm. & Ckll. ’03, p. 137 
cyathigerum 14+5 5-6 4 4-5 4+ | Tracheae only Lucas ’00, p. 297 
Walk. 16, p. 193 
ebrium 13+5.5 6 2-4 6 4+ | Tracheae only Walk. 14, p. 351 
Lyon ’15, p. 57 
exsulans 13+6 4-5 3 6-7 % Basal \% of Ndm. ’03, p. 255 
tracheae 
geminatum 1244.7 5 3 3-4 Y— | Tracheae only Ndm. '03, p. 254 
hageni 15+5 5 3 3-4 4%+ | Tracheae only Ndm. ’03, p. 253 
pallidum 14+7 4 2 6 4% Tracheae, base | Byers ’27, p. 00 
& apex 
praevarum 13+5 5 3 3 % Tracheae only Smn. '27, p. 14 
signatum 17+5.5 5 3 3-4 ? 3 dark bands Ndm. ’03, p. 258 
traviatum 11(?) +6} 4 6-7 2-3 0 Basal % Garm. '17, p. 556 
vesperum 16+5.5 5 3-4 4 0 Uniform (?) Walk. 13, p. 162 
(as pollutum) 

+ Body +¢gills. * Spines on outer margin of mentum of labium. 
t Spinous margin on base of dorsal edge of middle gill in terms of length of entire gill. 
The keys for the separation of the adults follow. A key dealing with 
sO many species is bound to be cumbersome, so final identification 
should only be made after a comparison with a written description and 
drawings of the male superior abdominal appendages. The identifica- 
tion of the females is notoriously difficult, and is in many cases only 
certain when the specimen has been taken mated with a known male, 
it is for this reason that collectors of Enallagma should be very careful 
not to separate such pairs in the killing and mounting processes. 
The species of Enallagma may be broken up into four large groups, 
based in the main on the genitalia of the male. These groups may be 
roughly defined as follows: 
Group A: Superior appendages distinctly shorter than the 10th ab- 
dominal segment; simple in form, not distinctly bifid, and without a 
tubercle. Color blue and black. Abdominal segment 2 with an apical 
black spot and ring, the remainder blue. 
