INSECUTOR INSCITI^ MENSTRUUS 119 



"Lower posterior margin of scuteUum with downward pro- 

 jecting hairs or pile." Sometimes the lower surface of the 

 scutellum has fairly abundant pile {CJiilosini) ; in certain groups 

 of Chrysogaster and in Apicomyia there is a single row of fine 

 silky hairs. Other genera treated here are without this 

 character. 



"Apical cross-vein forming right angles zvith the third vein." 

 The apical cross-vein changes its oblique course on its distal 

 end and turns upward, meeting the third vein vertically. The 

 upper distal corner of the first posterior cell is in form of a 

 right angle, likewise its complement. 



"Apical cross-vein forming an acute angle with the third 

 vein." The apical cross-vein continues its oblique course until 

 it meets the third vein. The first condition tends to be more 

 of the Chilosinae type, and has its extreme in the Chrysogaster 

 where it is even recurrent on its distal end. It occurs in a 

 number of the Chilosini and in Haw,m,erschmidtia. Microdon- 

 tinae also has this type of venation. The acute upper distal 

 corner of the first posterior cell is more characteristic of the 

 Xylotinae but occurs in a number of the Chilosinae as well. 



"Petiole beyond union of apical cross-vein and third vein 

 longer than length of discal cross-vein." This character at once 

 segregates the Chrysogasterini, Chilosini and Hammerschmidtia 

 from the other tuberculate Chilosinae. 



"Petiole beyond union of apical cross-vein and third vein 

 shorter than length of discal cross-vein." Occurs in the 

 Myioleptini. Another way of saying the upper distal corner of 

 first posterior cell is acute and close to the wing margin. 



"Pile on sternopleura." The distribution of the pile on the 

 sternopleura is dependent upon the development and move- 

 ments of the middle legs. Usually the upper third or fourth 

 region and the apex or lowest point is pilose and a bare smooth 

 space lies between. Malloch has pointed out that in Sphegina 

 the sternopleura is bare, while in Ncoascia the upper margin 

 is pilose, which is a good character for separating these closely 

 allied genera. 



