Occasional Papers of the Museum of Zoology 9 



in some terms of measurement or in the proportion of width 

 to length. Associated with wing narrowing is a reduction in 

 the size of the stigma (compare figures 3 and 4). But this 

 character, like narrowing, is difficult to express. The num- 

 ber of postquadrangular cells is an indefinite character, de- 

 pendent as it is on the variable position of the origin of M3 

 and an undiflferentiated cross-vein. M3 arises at or near the 

 subnodus, but varies in the same species. The proximal cross- 

 vein between jMs and M^ is the cross-vein which marks the 

 distal extension of the postquadrangular cells. But this cross- 

 vein has no specialized relation to the cross-veins posterior to 

 it, which form the ends of the postquadrangular cells, and it 

 may coincide with one of these or occupy any position be- 

 tween two of them. Thoracic and abdominal color patterns 

 are varied and usually of specific value. The common ground 

 color is some shade of orange-yellow; flesh, red, blue or 

 bluish and green or greenish are rarer. With the exception of 

 shining or metallic areas on the heads of some species, there 

 are no brilliant or metallic colors. With but rare exceptions 

 they are rather dull colored insects, and the females are prac- 

 tically all dull brown, obscurely patterned and inconspicuous. 

 Generally in group 2 the dorsum of the thorax is pale with a 

 middorsal black carina, which is universal in the genus, though 

 rarely reduced to a mere thread. The mesepimeron is often 

 largely dark, forming a conspicuous posthumeral dark stripe. 

 But in group 3, males of many species, which as tenerals have 

 a similar pale thoracic pattern, have the dorsum darken wdth 

 age till it may become entirely black. The color of the abdom- 

 en also undergoes some change with age, but it is slight and 

 does not result in a virtual loss of color pattern, as is the case 

 on the thorax. In males the third to fifth segments are usually 

 the most definitely and intricately patterned. This pattern is of 



