404 STUDIES IN AUSTRALIAN MECOPTERA, ii., 



we have, here, a fine criterion for determining whether any sup- 

 posed cross-vein is really such, or not. 



Let us apply this to the basal portion of Cuj, which, arching 

 up in the imaginal wing-\ enation to meet M, might well be mis- 

 taken for a cross- vein. From Text-fig. -3, we see that all the 

 cross-veins around it are destitute of macrotrichia. Not so this 

 vein, however; for it is seen to carry a series of closely-set macro- 

 trichia, which are continued along the rest of Cuj. 



Further, it will be seen that the macrotrichia de\eloped upon 

 the media are less in number than those upon the cubitus, for 

 any given length; those upon the cubitus being about twice as 

 luunerous. In this character also, the continuity of Cuj from 

 cuf'u]) to its fusion with M, and thence along the strong, con%ex 

 vein already mentioned, is clearly indicated. 



Putting the two sets of evidence together, there can be no 

 doubt that the correct interpretation of the condition of the 

 media and cubitus is that which is given in the Text-figures. 



Descrijytion of the Wing-Venation. (Text-fig. 4). 



Having solved the above problem, we can now name all parts 

 of the wing-venation without any doubt whatever. The result 

 is shown in Text-fig. 4. It will be seen that the wing-\'enational 

 type is essentially similar to that of the Lepidoptera, Trichoptera, 

 and Diptera, except for the fact that a considerable number of 

 unspecialised cross-veins are developed as supports between the 

 main veins. These cross-veins cannot be regarded as part of 

 the original venation, since they do not carry macrotrichia, and 

 are absent or very weakly developed in the oldest genera, both 

 fossil and recent. 



The Sabcosta {Sc) is a straight \ ein terminating about halfway 

 along the costal margin in the hindwing, somewhat beyond half- 

 way in the forewing. In Chorista, it gives off only a single 

 cross-vein in the costal space, near the base (occasionally, as in 

 Text-fig. 4, a second near its distal end). This is the homologue 

 of the humeral cross-vein in Lepidoptera and Trichoptera, and is 

 a true cross-vein, since it does not carry macrotrichia. 



