172 
DRAGONFLIES OF NORTH AMERICA 
Fore wing triangle crossed cross veins.......... Cordulia, p. 197 
Fore wing triangle free from.............. Dorocordulia, p. 198 
Nymphs 
Lateral setae four or five; mentum about as long as wide........ 
a Ridsetabcls Gascestile aati taeck Degeeca Caaete es 1 e Epicordulia, p. 175 
Lateral setae five or six: mentum longer. .Neurocordulia, p. 173 
Lateral setae seven; mentum of labium longer than wide...... 2. 
Abdomen with large, laterally flattened, generally cultriform dorsal 
GOMES io ce bcd odes abies mane da CP Galas 6 eee 3. 
Abdomen with no dorsal hooks, or with these rudimentary, not 
flattened laterally or cultriform, but small obtuse or pointed 
PYOMUINENCES...6 2 aii-ss » deesaine dves.a.Gve 4,5 cast aoe eee 5. 
Lateral spines of the ninth segment longer than half the length of 
that segment; dorsal hooks on segments 3-9, highest on 6, cul- 
LPILOPHT, ANC OMA oo. 2. sorckasuvancercce eee Tetragoneuria, p. 179 
Lateral spines of the ninth segment shorter than half of that seg- 
ment; dorsal hooks Jessideveloped: /a)4. -t......2.). ne 4, 
Dorsal hooks on segments 4—9 laterally flattened, but obtuse at 
apices, and not cultriform.............. Somatochlora, p. 184 
Dorsal hooks on segments 6-9, longest on 8 and cultriform...... 
5s chk n Dok, SI GAN Dean I an he ee Helocordulia, p. 182 
Hind angles of the head rounded; lateral spines of the ninth abdo- 
minal segment one-fifth as long as that segment............ 6. 
Hind angles of the head angulate superiorly; spines of the ninth 
abdominal segment one-third as long as that segment........ 
ATU STENT, Aa A ae ei a Dorocordulia, p. 198 
Teeth on lateral labial lobes deeply cut and separated by rather 
Wide NOCCHES.... . . i..052s0e he oe eee Somatochlora, p. 184 
Teeth low, separated only by shallow crenulations............. 
Cordulia, p. 197 
27. PLATYcORDULIA Williamson 
These are large yellowish cordulines with densely veined wings that 
are prettily spotted with yellow alongthe wholefront margin. The anal 
loop is widened at the end, where there is some doubling of the in- 
cluded cell rows, and two rows of cells intervene between the loop and 
margin of the hind wing. The superior appendages of the male are 
armed with a tooth on the inner side beneath their arched basal portion. 
The nymph is unknown. 
