38 PROCEEDINGS OF THE NATIONAL MUSEUM vol. so 



ternal characters. In a few the venation is unstable. This is par- 

 ticularly true of veins 2 and 3 of the fore wing of Semioscoj)is and 

 veins 3 and 4 of the hind wings of Agonopterix and Depressaria. The 

 genitalia of these three genera distinguish them, however, from all 

 others. The species fall, with one or two exceptions, into natural 

 groups on habitus as well as on structure, so that the definition of 

 genera is comparatively simple. 



In a few genera it is not entirely clear what we are dealing with. 

 For example, in Depressaria there are five distinct species groups, 

 which may actually represent separate genera. The leptotaeniae-mul- 

 tifdae group is especially interesting and represents a series of 

 "species" that may represent only simple Mendelian variants of oTie. 

 species. As will be noted, in the proper place, all these except yahiTmae. 

 are of practically the same color and have closely similar habits and 

 hosts, yet aU have distinct genitalia. 



In the genus Psilocorsis it is particularly difficult to separate many 

 of the species {re-ftexella-faginella group) , and here we are confronted 

 again with the problem of what actually constitutes a species. 



These problems can be settled only by careful breeding, and in the 

 meantime we shall have to content ourselves with the supposition that 

 genitalic differences represent specific entities or genera depending on 

 their nature. Nevertheless, I strongly suspect that Mendelian varia- 

 tion may be transmitted to the genitalia as well as other structures and 

 that eventually we shall be able in most instances to use genitalic 

 characters for group separation only. 



ACKNOWLEDGMENTS 



I wish to express my gratitude to August Busck, of the U. S. Bu- 

 reau of Entomology and Plant Quarantine, for suggesting this most 

 interesting study and for much advice and help received through 

 correspondence while I was at Washington State College and since I 

 came to the Bureau of Entomology and Plant Quarantine. To Dr. 

 R. L. Webster, Head of the Department of Zoology, Washington State 

 College, my sincere thanks are due for the use of his library and the 

 release from many duties which enabled me to do research and spend 

 much time in the field ; to Carl Heinrich for the larval diagnoses and 

 notes and for many helpful suggestions and much useful criticism; 

 to Dr. J. McDunnough, Chief of the Division of Systematic En- 

 tomology, Department of Agriculture, Ottawa, Canada; to Dr. 

 Annette F. Braun, Cincinnati, Ohio ; to H. H. Keif er, Department of 

 Agriculture, Sacramento, Calif.; and Mrs. Florence Blackmore, Vic- 

 toria, British Columbia, for much material lent for study; to Dr. 

 Lincoln Constance, Department of Botany, Washington State Col- 



