Dragon-flies and Damsel-flies 



89 



lengthwise one at each end of the body, are used by some. Specimens 

 intended for exchange should not be pinned up, but "papered," i.e., put 

 with folded wings into an enclosing little triangular paper envelope made 

 by folding an oblong paper sheet once diagonally and then folding over 

 slightly the two margins. 



Fig. 121. — Diagram of venation of wing of dragon-fly. a, antecubitals; 6, postcubitals; 

 N, nodus; P, pterostigma; ,'i, arculus; t, triangle, (.\fter Banks.) 



T.ABLES FOR CLASSIFICATION. 



Key to Suborders (Imagoes). 



Front and hind wings nearly similar in outline, and held vertically over the back 

 when at rest; head wide and with eyes projecting and constricted at base. 



(Damsel-flies.) Suborder Zygoptera. 



Front and hind wings dissimilar, hind wings usually being much wider at base, and 



both pairs held horizontally outstretched when at rest; eyes not projecting 



and constricted at base (Dragon-flies.) Suborder Anisoptera. 



Key to Suborders (Nymphs). 

 Posterior tip of abdomen bearing three, usually long, leaf-like tracheal gills. 



(Damsel-flies.) Suborder Zygoptera. 

 Posterior tip of abdomen with five, converging, short, spine-like appendages. 



(Dragon-flies.) Suborder Anisoptera. 



SUBORDER ZYGOPTERA. 



Key to Families (Imagoes). 



Wings with not less than five antecubital cross-veins (Fig. 121). 



Family Calopterygid.e. 

 Wings with not more than three, usually two, antecubitals (Fig. 121). 



Family Agrionid.d. 

 Key to Families (Nymphs). 



Basal segment of the antennae extremely elongate Family Calopterygid.e. 



Basal segment of the antennje short, subrotund Family .^grionid^. 



The family Calopterygidas includes but two genera, Calopteryx, in which 

 the basilar space of the wings is open and the wings themselves are rather 

 broad near the tip, and Hetasrina, in which the basilar space is net-veined 

 and the wings narrow. 



Calopteryx maculaia (Fig. 122), the most familiar representative in the 

 Eastern States of the first genus, has velvety black spoon-shaped wings, 



