vi 
INTEODUCTIOX. 
perhaps (in opposition to the views urged by the late Mons. Peyerimhoff in the 
'Annales de la Societe Entomologique de France,' 1876, p. 577) he depends too 
much upon the presence or absence of the costal fold for generic division, his 
critics have not yet produced any system of classification which can be said 
to supersede that of Heinemann, or to depart from the general guiding principles 
which he laid down. Many genera which have been perhaps linked together by 
the discovery of intermediate forms, or Avhich have not presented in themselves 
sufficiently strong permanent characteristic differences, besides some few, perhaps, 
which might possibly have remained clearly defined and acknowledged, seem to 
have been merged by him under more comprehensive generic titles, in which 
they have sunk to the rank of subgenera. It may be objected to this system that 
distinctions sufficient to separate the numerous subgenera are really equally 
sufficient to be of full generic value. 
Whilst following the method of determination laid down by Heinemann, I 
have ventured so far to depart from his system of arrangement for the purposes of 
this volume as to recognize his subgenera as genera, thus avoiding that departure 
from strict binominal nomenclature which is involved in the practice of writing 
names in such a form as Tortrix [Cacoecia) rosaceana, Harris;" and had I been 
following it less faithfully I should have been much disposed to break up the 
large genus Pwdisca into at least three separate divisions, which could, I think, 
be clearly defined. 
Heinemann uses Grapholitha, H.-S., as one of the subgenera of Grapliolitha, 
Tr. Since Heinemann's limitation of the subgenus is not exactly coextensive with 
Herrich-Schaffer's limitation of the genus, I have preferred to speak of Graiilio- 
litlia (H.-S.), Hein., as expressing that Heinemann's subgenus is adopted as distin- 
guished from the larger and more comprehensive genus of Treitsche. 
An additional reason for adopting Heinemann's method seems to be presented 
by the fact that Prof. C. H. Fernald, of Maine State College (who is, I believe, 
about to publish a complete list of the North-American Tortricidce), has been 
guided in his investigations by the rules laid down by Heinemann ; and as the 
present volume treats exclusively of North-American species, it will be found 
convenient that their classification corresponds, as far as possible, with that which 
has been adopted in compiling such a national catalogue. 
