AQUATIC INSECTS IN THE ADIRONDACKS 489 



from the grown nymph in this respect is sometimes (but very rarely) 

 true. Labium with four (less often five) lateral setae, and four larger 

 mental setae each side, with one or two lesser ones near the median line. 

 Thorax with broad sterna. 



Abdomen depressed, triquetral ; dorsal hooks large, cultriform, in a 

 very regular series, on segments 2-9 ; lateral spines on segments 8 and 9, 

 those of the ninth segment surpassing the level of the tips of the append- 

 ages; superior appendage very nearly as long as the inferiors, laterals a 

 little more than half as long as the inferiors. 



There are two indistinct and interrupted bands of brownish markings, 

 extending from the hind angles of the head to the bases of the spines on 

 the ninth abdominal segment, and there are darker rings on tibiae and 

 femora, discoverable specially after molting. 



This species M^as seen but a few times at Saranac Inn, and no speci- 

 mens were taken either as nymphs or imagos. It is not uncommon in 

 other places in the state, and will probably be found quite generally dis- 

 tributed when proper search is made for it. 



TETRAGONEURIA 



This North American genus is one of the most important, most 

 generally distributed, and most common in the subfamily. The imagos 

 are somewhat scarce in collections, but they are by no means so in 

 nature. Because of their superb aerial powers they are not often taken 

 in flight. They depart widely from the regular haunts of the less active 

 species while foraging, and thus often escape the specialist who is collect- 

 ing for dragon flies in particular. The roving habits of the imagos 

 account sufficiently for the wide distribution of most of our species. 



About an Illinois pond in which Epicordulia princeps and 

 Tetragoneuria cynosura were the only Cordulinae present, I 

 have watched day after day the little Tetragoneuria chasing the big 

 Epicordulia about in air, much as a kingbird chases and harasses a 

 crow, surpassing by its swiftness and by its ability to make quick 

 turns in air. 



Nymphs of this genus may be found in almost any pond ; they are 

 often found in enormous numbers. By far the easiest way to get imagos 

 is to capture well grown nymphs and rear them. 



Nymphs of this genus agree so closely that I give here a general 



account of them, which, for specific descriptions will only need to be 



supplemented by the specific characters stated in the following table; 



the differences therein stated are the only differences I know between the 



species. 



The nymphs are trim and smooth, with depressed abdomen and long 

 lateral spines. The general color is greenish or yellowish, with a 



