AQUATIC INSECTS IN THE ADIRONDACKS 485 



dd Wings clear ; inferior abdominal appendage of the male deeply bifur- 

 cated, the forks again notched at tips; never with less than five 

 antenodals in the hind wing, or with the triangle of that wing 



traversed by a cross vein Cordulia 



cc Triangles of the fore wings open - D oroc or dul ia 



So well marked are these genera that they may generally be recognized 

 at a glance by the following. 



Single distinctive characters 

 Epicordulia alone has large brown spots at base, nodus and stigma 



of all wings. 

 Tetragoneuria alone has but four antenodals in the hind wing. 

 Helocordulia alone has the stigma very narrowly diamond-shaped, 



with the ends of it meeting the sides by an angle of 3o°-35°. 

 C o r d u 1 i a alone has the inferior abdominal appendage of the male 



deeply bifurcated. 

 Dorocordulia alone has the triangle of the fore wing free from cross 



veins. 

 Neurocordulia has been sufficiently distinguished above ; S o m a t - 



o c h 1 o r a possesses none of the characters of this list. 



Nymphs 



a Lateral setae four or five ; mentum about as long as wide. . Epicordulia 



aa Lateral setae seven ; mentum of labium longer than wide 



& Abdomen with large, laterally flattened, generally cultriform dorsal hooks 



c Lateral spines of the ninth segment longer than half the length of that 



segment ; dorsal hooks on segments 3-9, highest on 6, cultriform, and 



sharp Tetragoneuria 



cc Lateral spines of the ninth segment shorter than half of that segment; 

 dorsal hooks less developed 

 d Dorsal hooks on segments 4-9 laterally flattened, but obtuse at apices, 



and not cultriform Somatochlorai 



dd Dorsal hooks on segments 6-9, longest on 8 and cultriform 



Helocordulia 

 Ih Abdomen with no dorsal hooks, or with these rudimentary, not flattened 

 laterally or cultriform, but small obtuse or pointed prominences 

 c Hind angles of the head rounded ; lateral spines of the ninth abdominal 



segment one fifth as long as that segment Cordulia 



cc Hind angles of the head angulate superiorly ; spines of the ninth abdom- 

 inal segment one third as long as that segment Dorocordulia 



1 There can be little doubt that the unknown nymphs of the numerous species of this genus will 

 necessitate an amplification of the characters herein stated. S. elongata appears to be the only 

 American species yet reared. Cabot described a nymph as that ofSom. alblcincta, supposition, 

 but I am unable to say whether the supposition was correct : so far as one may judge from his figure, 

 that one might as well have been Cordulia shurtleffl. The typical Somatochlora 

 me tallica of Europe has dorsal hooks on segments 3-9 of abdomen, with the posterior ones bet- 

 ter developed than in S. e 1 o n g a t a . It must be borne in mind by those who use this table that it 

 is based only on the nymphs of the species herein described. 



