468 THE STUDY OF INSECTS. 



remembered, however, that these flies are long-legged in 

 comparison with the allied families, and not in comparison 

 with crane-flies and midges. 



The members of this family are easily distinguished as 

 such by the peculiar venation of the wings, the most char- 

 acteristic features of which are the following (Fig. 571): 

 cells V and ist V 2 are not separated by a vein, the basal 

 part of vein V 3 being undeveloped ; veins III a+3 and III 4+B 

 separate near the base of the wing, and the two veins form 



nil 



-^. 



+3 



+ VII, 



FIG. 571. Wing of Psilophus ciliatus. 



at the point of separation a more or less knot-shaped swell- 

 ing; the cross-vein III-V is at or close by this swelling, so 

 that cell III is very short. A somewhat similar venation 

 occurs in some of the Muscidae ; but there the knot-shaped 

 swelling on vein III is often wanting, and the cross-vein 

 Ill-Vis usually more remote from the base of the wing; 

 and too the flies belonging to the Muscidas possess the 

 suture above the antennae characteristic of the suborder Cy- 

 clorrhapha. 



The members of this family have three ocelli ; the an- 

 tennae are three-jointed ; the second segment of the antenna 

 is sometimes rudimentary ; and the third segment bears a 

 two-jointed arista. 



The adults are predaceous and hunt for smaller flies and 



