The ecologist who travels through Texas and Oklahoma might assume that the area could be easily divided into regions which are biotically distinct. The transitions from humid east to arid west and from subtropical south to cool north produce some very obvious patterns of distribution of flora and fauna. In spite of this obvious pattern, published records indicate many differences of opinion on both the location and description of the biogeographic regions or major biotic communities of these states. A few of these differences are more apparent than real because of variations in terminology or intensity of investigation. Other differences can be interpreted only as fundamental disagreements on what constitutes a major biotic community. The question that has not been answered is: how different must the fauna and flora of two areas be before they are recognized as examples of different communities? Many of the differences result from attempts to separate communities by a line drawn on a map. Typical examples of communities are relatively easy to separate, but the separation is difficult in the gradual transitions or ecotones between communities. For example, Taylor ('45) lists 28 species of mammals as characteristic of Eastern Texas. A composite map of the ranges of these species emphasizes that no two species have identical limits of distribution. The short-tailed shrew (Blarina brevicauda) is limited to the extreme eastern portion of Texas; the gray squirrel (Sciurus carolinensis) oc-