232 DRAGONFLIES OF NORTH AMERICA 
varying from almost none at all to half the wing extent, and the veins 
are often red. 
These are the latest of our dragonflies in season. One of our species 
S. corruptum is sometimes taken in early spring, having hibernated as 
an adult. They are pond species and the swales adjacent to the shoals 
are the best places to find them. They fly moderately and rest fre- 
quently on the low vegetation and are not very hard to capture. 
The females of some species lay their eggs upon floating masses of 
“blanket algae’? where, exposed more or less to the air, they become 
infested with minute Hymenopterous parasites. 
KEY TO THE SPECIES 
Adults 
1 Fourth abdominal segment with a median encircling ridge (in 
addition to theapical'ridge).. se P20. Pe: ee ee a. 
Fourth abdominal segment with only the apical ridge......... 3. 
2 Fore wing, antenodals 7; sides of thorax with two white stripes 
BBs eh hah a mrt OE ALON | LEUE TGS iad OR MO corruptum, p. 233 
Fore wing, antenodals 8 to 10; sides of thorax with two white 
BOLUS. 5 Cee meres a ae el itn an SBLOT Cn oe ae eee illotum, p. 233 
3 The radial planate subtends two rows of cells...madidum, p. 234 
The radial planate subtends but a single row of cells.......... 4. 
4 Expanse more than 70 mm............. ..furcatum, p. 234 
Pxpanse less. fhan/GO) mpi. isch i. oh veflillie's, dere, 0s eee a a 
5 Male superior appendages with a prominent median inferior tooth; 
female subgenital plate bifid’ 0.522069 .3 tae 8. 
Male superior appendages with no prominent inferior tooth (with 
only denticles); female subgenital plate entire or only a little 
EMATOINATE so cfs Boe a ee ede Pee ree tae eae 6. 
Gi. Tibia, yellow, externally:.\4-c04 3, uctae tg eee ie ne a re 
Tibiae black oxternallyis.)... 8 2..5.° 7 toy es es a 10. 
7 Abdomen with black markings.............. ambiguum, p. 235 
Abdomen with yellowish brown markings........ pallipes, p. 235 
8 Male bifid for a third of its length, the outer branch twice as stout 
GS, the IWMER. oe oe )s ayes ¥ odes gar as ein tote es Re 9. 
Male hamule bifid for not more than a fourth of its length, the 
outer branch four times as stout as the inner. .obtrusum, p. 236 
9 Wings yellow only at the roots........... rubicundulum, p. 236 
Wings with basal half yellow............... assimilatum, p. 237 
