No. 39] ODONATA OF CONNECTICUT: LIBELLULIDAE 199 



Nymphs of the family are in general characterized by the mask- 

 like labium which covers the front of the head up to the antennae. 



Adults also have a mask, the palpi meeting in a line on the 

 meson. 



Subfamily Cordulinae 



1. Macromiini Macromia, Didymops 



2. EucoRDULiiNi Somatochlora, CorduUa, Tctragoneuria, 



Neuro-, Doro-, Helo- and Epicordulia, 

 Williamsonia 



Subfamily Libellulinae 



1. Libellulini Plathemis, Lihellula 



2. Palpopleurini Perithemis 



3. Brachydiplacini Nannothcmis 



4. Sympetrini Erythrodiplax, Pachydiplax, Sympetrum, 



Erythemis, Celithemis, Leucorrhinia 



5. Trameini Tramea, Pantala 



Subfamilies Cordulinae and Libellulinae 



Key to Tribes 

 Nymphs 



1. Head with a prominent frontal horn MACROMnNi, p. 201 



Head without a prominent frontal horn 2 



2. Lateral spines of abdominal segment 8 as long as segment 9 or 



longer; without dorsal hooks on 5-7 Trameini, p. 288 



Lateral spines of abdominal segment 8 shorter than the length of 

 segment 9 or absent ; if with long lateral spines as above, then 

 with dorsal hooks on segments 5-7 3 



3. Superior terminal appendage as long as the inferiors (Nannothe- 



mis) Brach YDiPLACTNi, p. 259 



Superior terminal appendage not so long as the inferiors 4 



4. Length of the labial palpus from lateral point of articulation with 



the mentum to base of movable spine or hook (distal segment 

 one-fourth to one-fifth longer than the distance from the articu- 

 lation to the internal angle) ; also longer than the distance from 

 the point of articulation to the base of the mentum (Fig. 66) 



(Perithemis) Palpopleurini, p. 257 

 Length of labial palpus from lateral point of articulation with the 

 mentum to base of movable spine or hook usually shorter than 

 the distance from articulation to the internal angle (occasionally 

 slightly longer but not one-fourth or one-fifth longer) ; usually 

 shorter than the distance from the articulation to the base of 

 mentum 5 



5. Length of segment 10 plus the terminal appendages measured on 



the mid-ventral line shorter than segment 9 ; lateral terminals 

 nearly or quite as long as the dorsal, never less than half as long 



Eucorduliini, p. 206 

 Length of segment 10 plus the terminal appendages measured on 

 the mid-ventral line as long or longer than segment 9 ; lateral 

 terminals usually not over half as long as the dorsal 6 



