62 
Indiana University Studies 
Author 
Species assigned 
Accepted in pre- 
to present genus 
sent revision 
Mayr 1870-1905 
17 
88 per cent 
Dalla Torre 1893 
42 
48 per cent 
D. T. and K. 1902 
50 
46 per cent 
D. T. and K. 1910 
68 
41 per cent 
Beutenmuller 1911 
43 
32 . 5 per cent 
Weld 1922-26 
46 
37 per cent 
Our present delimitation of Cynips is based upon no single 
character — indeed, we know of no character by which the 
group may be separated from other groups of oak-inhabiting 
Cynipidae — but upon a striking, even if not invariable, corre- 
lation of insect structures, gall characters, host relationships, 
life histories, and distributional data that are coordinated for 
the 93 species which we now bring together. 
In nearly every one of the species the agamic form has the thorax 
hairy, altho there are few hairs on the very small, nearly wingless in- 
sects which are the most northern varieties of many of the European 
and American species in Cynips. In every species without exception the 
hypopygial spine is broadest posteriorly, and the structure terminates in 
a well-developed tuft of hairs. A similar spine is found, however, in one 
or two related genera. In 90 of the species the tarsal claw is rather 
strongly toothed, but in 3 species of a single stock (Cynips mellea) the 
claw is so weakly toothed that it is nearly simple. In nearly all of the 
species the agamic gall is fundamentally spherical and monothalamous, 
rarely with any remarkable development of the epidermal layer of 
tissues; but in 8 species of one stock (Cynips pezomachoides) the gall is 
usually polythalamous. In every one of the 93 species the gall originates 
from leaf veins, usually on the under surface of the leaf, but in two 
species (C. multipunctata group) the gall may occur on the leaf petioles 
and young stems as well as on the leaf. In every one of the 11 species 
for which the alternating generations are known, the bisexual gall is a 
thin-walled, seed-like or bladdery, hollow cell located within the newly 
opened buds of the oaks. All of the 93 species occur on white oaks 
( Leucobalanus) . In nearly every case the agamic generation begins de- 
velopment in early summer, matures by early fall, lies as an adult within 
the gall for several weeks or months, and finally emerges in the winter. 
Only the 7 species of the fulvicollis stock modify this procedure by de- 
laying part of the emergence until a second or later winter. Some of 
the species of the mellea stock also depart from the typical life history 
by emerging in the early spring instead of the winter season. In dis- 
tribution the insects show their affinities by occurring in adjacent areas, 
