286 DRAGONFLIES OF NORTH AMERICA 
and hard to observe, but of very great importance taxonomically as 
are also the mesostigmal plates (laminae) of the females. Figures of 
both are given with the descriptions that follow. 
The nymphs of Argia are usually recognizable at a glance by reason 
of their thick set bodies and the dark colored, short, broad gills. If 
this is not sufficient, the entire absence of mental setae will serve to 
separate the members of this genus from all the following Coenagrioni- 
nae. The nymphs of the 9 known species are so very much alike that 
a short generic description will be given for them all, followed by a 
table giving the characteristics more or less peculiar to the species. 
The nymph is short and thick and usually with dark colored legs 
and short oblong gill plates. The head is somewhat wider than long, 
flat above with very prominent eyes. The antennae are six or seven 
jointed, the third joint being the longest. The labium is short with the 
hinge reaching barely to the base of the middle legs; the median lobe 
is without mental setae but has a row of small setae on the lateral 
margins just posterior to the articulation of the lateral lobes: lateral 
setae 1-4; lateral lobe short with a short stout moveable hook and a 
small end hook which may or may not be separated from the inner 
margin by a notch (see column 5 of the table). Abdomen stout, some- 
The Known Nymphs 
Gills 
Species Mera ger Oe IN cp Described by 
set. Greatest E 
breadth augment 
agrioides 12+6 2-4 absent near m. mottled Smn. ’26, p. 13 
apicalis 14+6 3-4 present middle 3 x bands Ndm. ’03, p. 242 
emma 17+5 1 present before m. az bands Kndy. ’15, p. 271 
fumipennis 10+4 2-3 absent middle 1 x band Ndm. ’04, p. 714 
moesta 14+5-6 1 present before m. uniform Ndm. & Ckll. ’03, p.136 
sedula 12+4 2; absent middle uniform Smn. ’26, p. 13 
tibialis 12+4.5 4 absent beyond m. apical Ndm. ’03, p. 244 
translata 13+5 1 present beyond m. 3 confluent Brtn. '28, p. 34 
ax bands 
violacea 17(?) +4.5 | 2-3 present beyond m. V-shaped Ndm. ’03, p. 242 
apical 
vivida 12+3 4 absent Kndy. ’15, p. 288 
* Body + gills. 
** Tn end of lateral lobe separating off the end hook. 
what tapering, with its segments decreasing in length to the ninth, 
the tenth again a little longer. Gills oblong about half as wide as long. 
The shape and pigmentation of the gills varies with the species as 
indicated in the table. 
