first joint short and the two following of equal length; the 

 last one longer and more slender than the preceding. 

 Thorax arched, without suture; the scutellum small. Ab- 

 domen cylindrical, composed of seven or eight segments; 

 genitalia concealed ; legs strong and not elongated ; fe- 

 mora broad and flat: tibiae usually with terminal spurs ; 

 first joint of the tarsi longer than the following and usu- 

 ally dilated in the male; the last joint small. Wings 

 large and broad, with distinct alulae, anterior veins thick- 

 ened, the others slender; auxiliary vein terminating in 

 the costa about the middle of the wing; second longi- 

 tudinal vein wanting, the first and third lying close to 

 each other; the third arising from the first rectangularly 

 before the end of the auxiliary vein ; anterior cross-vein 

 very short; fourth vein curved, forked nearly opposite 

 the anterior cross- vein; the forks terminating near the 

 tip of the wing. 



Fig. 44. Sium/iiitn rennstmn, enlarged. After Washburn. 



