499 



Males possessed by the Illinois State Laboratory of Natural His- 

 tory were collected at Cedar Lake, 111., — Lake Villa — August 3, 1887. 

 The female was described from material obtained from Mr. E. B. 

 Williamson. 



The species has not been seen as far south as Urbana. 



Subfamily COENAGRIONINAE 



The nymphs have short labia, gradually contracted proximad and 

 not at all spoon-like. The gills are more or less lanceolate, acutely 

 pointed at the tip, and the smaller tracheae are commonly well devel- 

 oped, pigmented, and visible to the naked eye. The abdomen is short 

 in proportion to its diameter. 



The adults are distinguished from the Lestinae by means of the 

 wing venation, M 3 arising nearer the nodus than the arculus. The 

 femoral and tibial setae are much shorter than those of the Lestinae 

 and the coloration of the body is frequently bright, the yellows, blues, 

 and reds being often conspicuous. The anal appendages of the male 

 are short and the eighth sternites at the base of the cephalic pair of 

 gonapophyses of the female are reduced to small triangles or are want- 

 ing. 



Key to Genera 



nymphs 



a. Gills half as broad as long (Figs. 58, 63, 67, 68) ; labium without 

 mental setae ; proximal segment of the labial palpus with two similar 



fixed hooks Argia. 



aa. Gills not more than one-third as broad as long ; labium provided 



with mental setae; proximal segment of the palpus with a single, 



sharp, fixed hook, and a truncate process with teeth at the apex. 



b. Caudo-lateral angles of the head projecting and forming a blunt 



tubercle, the margins of the head much contracted between the 



tubercles and the eyes. 



c. Gills (Fig. 59) without cuticular pigment, one-third as broad 

 as long, the margins thickly provided with setae which extend 



from the base to the apex of the gills Ampliiagrion. 



cc. Gills with cuticular pigment, not more than one-sixth as broad 



as long, the margins sparsely setose Chroma grion. 



bb. Caudo-lateral angles of the head not projecting and forming a 

 blunt tubercle, the margins of the head not contracted between the 

 tubercles and the eyes. 



c. Gills with the tracheal branches much more numerous at the 

 widest portion of the gill Nehalennia. 



