Kinsey : Gall Wasp Genus Cynips 
71 
of the insects of the Coast Ranges have northern varieties 
that reach their southern limits and southern varieties that 
reach their northern limits near San Francisco Bay. If the 
migration in such cases had been wholly from the north or 
wholly from the south, it is not easy to understand why the 
break should occur near San Francisco Bay; but the situa- 
tion is explainable if it is presumed that both stocks origi- 
nated from the eastern Sierras, that the northern variety 
reached San Francisco Bay from the north and the southern 
variety from the south, and that the Bay never was crossed 
until a geologically recent day. 
The Eastern American group of subgenera of Cynips was 
differentiated in the late Miocene or early Pliocene, as the 
following considerations may show. 
None of these subgenera are represented west of the Great 
Basin today, and it is probable that they were prevented from 
reaching the Sierras by the development of the Great Basin 
deserts in the Miocene. 
That the subgenera were distinct and most if not all of the 
present-day species differentiated before the end of the 
Pliocene is attested by the fact that all but one of the species 
found east of the Great Plains is represented by close rela- 
tives, either very closely related species or varieties of the 
same species, in the Rocky Mountain area. The following 
table summarizes the situation. 
Eastern Species 
Rocky Mountain Relatives 
C. fulvicollis 
C. plumbed 
C. centricola 
C. dugesi and C. bella 
C. pezomachoides 
C. pezomachoides, 1 variety 
C. gemmula 
Not known 
C. hirta 
C. hirta, 2 varieties 
C. villosa 
C. villosa, 5 varieties 
C. mellea 
C. mellea, 1 variety; and C. arida 
This eastern extension of the Rocky Mountain fauna must 
have occurred before the Rockies reached their heights and 
thus caused the aridity of the Great Plains in the Pliocene. 
Today, between the easternmost oaks in Colorado and the 
westernmost extension of oaks in Kansas there are three or 
