508 NEW YORK STATE MUSEUM 



/Male with no ventral books on the first abdominal segment; 

 female with the hind tibia a little longer thau the hind femur; 



the sexes alike in wing pattern Libellula p. 530 



ff Male with a pair of ventral hooks on the first abdomiaal segment; 

 female with the hind femur and tibia of equal length ; wings 



dissimilarly colored in the two sexes Plathemis p. 536 



cc Triangle of the fore wing placed beyond the level of the apex of the 



triangle of the hind wing; stigma with its inner end perpendicular, its 



outer end very oblique to the bordering veins ; wiogs broad at base 



and pointed at apex 



d Radial sector regularly curved; hind wings with a broad, basal colored 



baud Tram e a p. 537 



M Radial sector distinctly undulate; hind wings not covered at base by 

 a broad colored band Fantala p. 539 



Nymphs 



a Unknown Nannothemisi and Micrathyria 



aa With large, cultriform dorsal hooks on abdominal segments 3-9 ; eyes small 

 and situated on the midlateral margin of the head and directed laterally 



Perithemis 



aaa With no dorsal hook on the ninth abdominal segment: eyes overspreading 



more or less the anterolateral margins of the head 



h Basal segment of the hind tarsus more than half as long as the second 



segment; lateral appendages of the abdomen not more than half as long 



as the inferiors (except in Libellula quadrimaculata); superior 



abdominal appendage regularly tapering to a point 



c Abdominal appendages strongly decurved; lateral spines wanting or 



extremely rudimentary Mesothemis 



cc Abdominal appendages straight or very slightly declined; lateral spines 

 evident on abdominal segments 8 and 9 

 d With no dorsal hooks at all ; abdomen smooth, depressed ; head twice as 

 wide as long, with eyes very prominent laterally.. Pachy diplax 

 dd Dorsal hooks present, at least on the middle abdominal segments 

 e Abdomen ovate in outline, rather abruptly narrowed to the posterior 

 end ; hind margin of the eyes behind the middle of the head 

 / Lateral spines long and straight ; abdomen not narrowed posteriorly 



before the eighth segment Celithemis 



ff Lateral spines shorter and more or less incurvate ; the abdomen 

 more or less narrowed before the eighth segment 

 g Dorsal hooks as long as the segments which bear them 



Leucorhinia 

 gg Dorsal hooks shorter than the segments which bear them 



Sympe trum 



ee Abdomen lanceolate in outline, slowly narrowed to the pointed 



liosterior end ; eyes capping the prominent anterolateral angles of 



the head, their hind margin generally before the middle of the top 



of the head; body generally hairy 



1 Discovered since this key was prepared, and described below under the account of the genus. 



