Page:The Gall Wasp Genus Cynips.pdf/74

 The close affinities of the Eurasian and Pacific American subgenera of Cynips, and the more unique nature of the eastern American subgenera suggests that the migration between Eurasia and North America was by way of the Alaskan-Siberian land bridge, rather than by way of former land connections between Labrador, Greenland, Iceland, and northern Europe. The migration of the first group of Cynips

from its center of origin in the Southwest, to our Pacific Coast, and finally across Alaska into Siberia, must have occurred before the Great Basin became arid, and while the Alaskan-Siberian land connections were still enjoying a climate mild enough to have supported an oak forest. From the preceding table it will be seen that fossil oaks are known to have occurred in both Siberia and Alaska as late as the Eocene, and the land connections between the two continents were continuous thru the late Miocene and intermittently existent at later periods. Berry, however, expresses it as his