OF WASHINGTON, VOLUME XVI, 1014 .11 



Lcpidoptera, except in a small group of families, which until 

 recently has been associated with, and derived from the Tineidie, 

 but which, on this character alone must be placed, as Spuler has 

 done, quite apart from the other non-aculeate Microlepidoptera. 



The development of the venation is towards the reduction of 

 the number of veins, mainly by coalescence, though frequently 

 by becoming obsolete, and this is the guiding principle in the 

 classification. Thus a genus with all the veins present cannot be 

 deduced from one with a less number of veins, according to the 

 fundamental law that a lost character cannot be regained. Simi- 

 larly, a genus with two veins separate cannot normally be de- 

 rived from one in which these two veins are stalked, that is, 

 partly coalescent. 



The reduction of veins has gone on in all branches of the system 

 of families, but reaches its climax in the genus Opostega, where 

 all but a few principal longitudinal veins have become obsolete. 

 In it we have a striking case of an apparently "simplest" form, 

 which in reality is the most highly developed in the group. 



A very different result from the same tendency to vein reduction 

 is found in the Cosmopterygidse, where the number of veins in 

 some genera has been preserved, but where several of the veins 

 have coalesced at base on account of the wings becoming very 

 narrow and pointed, producing a many branched venation. 



On these principles the present system has been built up, not 

 that the venation alone has been used (in fact, most of the 

 genera were made on other characters entirely, long before the 

 value of venation was realized) but the vein characters are now 

 used as the final test. If two speciesVary in any essential of the 

 venation, they are separated generically on that character alone, 

 even should they agree in all other characters. 



However, the venation, as well as any other character, must 

 be used with good sense, and only one thoroughly familiar with 

 the group as a whole, is safe in applying the test in the numerous 

 difficulties which occur. 



Thus a character may be an essential one in a higher developed 

 group of genera and of relative unimportance in a more generalized 

 group which has not .yet acquired the same constancy. In the 

 Gelechiidse, Xyloryctidae, OEcophoridae and Cosmopterygidae, for 

 example, veins 7 and 8 of the fore-wings are invariably stalked, 

 or coincident without exceptions,, but in lower groups, like the 

 Plutellidae or Acrolophidse, these same veins may be stalked 'or 

 separate within the same genus or even within the same species, 

 and consequently cannot be given the same value here as in tin- 

 higher groups. But it should be noted that even with this varia- 

 bility, the venation furnishes sufficient stable characters in the 



