likely to have ranged in any force into a cold-temperate or boreal environment. In view of these conclusions it seems doubtful whether _Eumeces_ or other reptiles could have crossed the Alaskan-Siberian land connection so late as the Miocene. On the contrary, the climate and habitat conditions with which _Eumeces_ might have been associated, although present as far north as Alaska in the Eocene, evidently had shifted far to the south by mid-Tertiary time. Axelrod (1950:230) has described a Miocene forest of the Columbia Plateau and northern Great Basin indicative of a uniform temperate climate and an average rainfall of thirty-five to sixty inches. This forest included: (_a_) various genera now characteristic of the southeastern hardwood forest or confined to it--_Carya_, _Castanea_, _Comptonia_, _Fagus_, _Liquidambar_, _Nyssa_, _Taxodium_; (_b_) other genera at present more characteristic of the western United States--_Sequoia_, _Lithocarpus_, _Pseudotsuga_, _Mahonia_, _Thuja_, _Gaultheria_, _Amelanchier_; (_c_) wide-ranging genera including _Alnus_, _Acer_, _Betula_, _Populus_, _Quercus_, _Picea_, _Pinus_, _Tsuga_, _Cornus_, _Ribes_, _Rosa_, _Hydrangea_; (_d_) modern east Asian genera, including _Ginkgo_, _Ailanthus_, _Glyptostrobus_, _Keteleria_, _Koelreuteria_, _Metasequoia_, _Pseudolarix_, _Pterocarya_, _Zelkova_, which were eliminated from the North American flora in the latter part of the Tertiary. In short, this western Miocene forest was remarkably similar in many respects both to the presumably ancestral early Tertiary Alaskan forest and the modern southeastern hardwood forest. The extent of this Miocene forest is unknown but judging from the sites where it has been recorded, it had progressed about halfway, both in latitude and in actual distance, from Alaska to the area occupied by the modern southeastern deciduous forests. Several other reptilian genera have distributions similar to that of the _fasciatus_ group, with representatives in southeastern Asia and southeastern North America that probably have parallel histories of distributional divergence from early Tertiary northern ancestors similar to contemporary species (Schmidt, 1946:148-150). _Alligator_, _Natrix_, _Ancistrodon_, _Scincella_, _Elaphe_, _Opheodrys_, and within the genus _Eumeces_, the _obsoletus_ group, all provide excellent examples. EFFECT OF CLIMATIC FACTORS