604 



NEUIIOPTERA. 



in having the anal angle of the posterior wings of the male 

 acute, u^schna heros Fabr. is one of our largest and most 

 abundant dragon-flies. It is fuscous, marked with yellowish 

 green, and with two oblique green stripes on the side of the 

 thorax. 



In the third gi'oup of this immense family, the Libellulina, 

 the wings are unequal, and the triangle of the anterior wings 



Fig. 588. 



is dissimilar, while the anterior genital hamule of the male is 

 free. In Cordidia the anal angle of the posterior wings of the 

 male is acute, and the body is brassy green. C. tenebrosa Say 



is found in the Western 

 States. 



The genus LibeUuIa is 

 characterized by the short, 

 rather flattened abdomen, 

 narrowing rapidly towards 

 the tip, and the male clasp- 

 ing organs are scarcely visi- 

 ble. Libellula trimaculata 

 DeGeer (Fig. 587, male) is 

 'P'^s-589. g^j g^||g(| fj-on^ the three 



dark clouds on the wings of the female. The male diflTers in 

 having a dark patch at the front edge of the wings, and a sin- 

 gle broad cloud just beyond the middle of the wing. Libel- 



