82 NORTH AMERICAN DIPTERA. 



gated, whiplash-like. Thorax convex above, with a very 

 distinct suture in the form of a shallow V, except in the 

 Ptychopterinse ; prothorax usually distinct, collar-like; 

 scutellum half-round; metanotum strongly developed. 

 Abdomen cylindrical, composed of seven or eight joints; 

 genitalia prominent, in the male very variable in struc- 

 ture ; in the female, the ovipositor (save rarely) has two 

 pairs of long, horny, pointed valves. Legs very long 

 and slender; the tibiae sometimes with terminal spurs. 



Fig. 24. Venation. 



Wings long, but comparatively narrow; in rest spread 

 apart or lying parallel over the abdomen ; auxiliary vein 

 present; always six longitudinal veins; usually a com- 

 plete discal cell; both basal cells long; the anal cell 

 usually widely open; seventh vein usually distinct (save 

 in the Ptychopterinae) and of variable form; axillary 

 lobe rounded, rarely angular. 



The family Tipulidse comprises the largest of the 

 nematocerous flies, some of which exceed two inches in 

 length. The abdomen is always elongate. The legs are 

 very long and delicate so delicate indeed that one sel- 

 dom succeeds in capturing the insects without the loss 

 of one or more. Flies of this description with a distinctly 

 impressed V-shaped 'suture' on the mesonotum will be 

 immediately recognized as belonging to this family. The 

 females differ from those of most other flies in having the 

 ovipositor adapted for the deposition of their eggs in the 

 ground or other firm substances. When the weather is 



