INTRODUCTION. vil 
innumerable and minute variations as to be quite unreliable for the purpose of logical 
differentiation. 
In the Acrolophidae again, as already pointed out (vide pp. 378-80), the position 
and length of the male palpi, which had been greatly relied upon, vary by the most 
gradual and perplexing stages, so that it may well be said in words which I extract 
from a letter in English long since received from the late Professor Zeller “the 
passages from which to it” form a chain of evidence too strong to be broken down in 
any attempt to separate extreme forms. 
In the Tortricidae the costal fold, although a purely sexual character, was a 
convenient mark of recognition frequently regarded as of generic value ; but this occurs 
sporadically among many species which, although undoubtedly distinct, present no 
other structural peculiarities to justify their inclusion in different genera—notwith- 
standing the fact that this character is apparently consistent in whichever species may 
possess it. 
Central American representatives of the Zineina are to be found in at. least 
22 families, of which the Gelechiadae with 228 species, and the Stenomidae with 144, 
afford more abundant examples than others. Among these the Gelechiadae may be 
said to extend in approximately equal numbers to north and south, although the 
southern or South American forms are for the most part distinguished from those of 
the United States and Canada by their affinities to such genera as Strodisia Clms., 
Anacampsis Crt., and Dichomeris Hb., the first of these unrepresented in Europe, 
whereas the northern forms are more obviously allied to those of the European fauna. 
The Stenomidae, again, accompany the Gelechiadae in both directions, but tend strongly 
to represent the southern rather than the northern fauna, and the same may be said 
of the Hyponomeutidae ; whereas the Vemophoridae, well represented in more northern 
latitudes, vanish entirely to the south of Panama, reappearing in certain limited forms 
to the far south of the continent. The Acrolophidae, strictly confined to the two 
American continents and to the West Indian Islands, are perhaps pre-eminently 
tropical, but with considerable southern and northern extension—this very distinctly 
recognisable family has afforded strong evidence in favour of discarding secondary 
sexual characters when determining the limitation of genera. The Acrolophidce, after 
an immense amount of careful work involving the examination of many hundreds of 
specimens, are found to consist practically of one large genus, represented by many 
species, in some of which the neuration is so variable as to forbid the establishment 
of genera upon the numbers, position, or furcation of veins in the radial or median 
series of the forewings. The species can, however, be distinguished inter se by the 
length and position of the labial palpi, by the structure of the antennae, and by the 
