24 
Indiana University Studies 
previous paragraphs, related varieties of a species are to be 
expected on each of the oaks of any group of oaks affected; 
and since not more than one variety ordinarily occurs on 
each of these oaks in a single faunal area; and since each 
of the faunal areas of the United States will have a distinct 
variety if the host of the insect is found in that area: then, 
giving each oak a number representing the faunal areas in 
which it occurs, and adding the numbers of all the species 
of the group or groups affected by the Neuroterus species, 
we should have the number of the possible varieties. There 
are a number of factors which interfere with the use of this 
method, and thruout I have tried to be very conservative in 
making estimates. Thus, I have not considered two geo- 
graphic regions distinct unless I have abundant data which 
indicate that we never get the same cynipid from the two. 
I have not considered two oaks distinct in these connections 
if we ever get the same cynipid on them. Thus, I have con- 
sidered Q, lobata and Q. Douglasii as one thruout these esti- 
mates-; Q. durata is not counted distinct from dumosa; Q. 
stellata and Q. breviloba may have the same faunas in their 
more eastern Texas ranges ; Q. stellata, Q. Chapmanii, and Q. 
Margaretta have been counted as one in the extreme southeast. 
My interpretations of faunal areas and oaks have been based 
on my data for all groups of Cynipidge, and not on Neuroterus 
alone. On a whole it is very probable that these estimates 
are not too high, even when they total the figure of about 
680 varieties possible in the United States for the 16 species 
now known. The detailed estimates are given with the de- 
scriptions of each of the species. 
Allowing for the discovery of additional species, the ex- 
ploration of Mexico, the addition of Europe, Asia, and par- 
ticularly southeastern Asia, we may estimate that a thousand 
different living insects belong to this genus. Only about 83, 
or 8 per cent, are yet described from the whole world! Of 
the 680 estimated for the United States, only 9 per cent are 
known in spite of the collecting we have already done here. 
How true a reflection may this be of our knowledge of insects 
in general? I am inclined to think it is nearer an average 
than is generally believed. It is true that the development 
of distinct varieties is favored in the Cynipidse by their host 
isolations, but the same is often true of other phytophagous 
