VARIATIONS AND RELATIONSHIPS IN THE SNAKES OF THE GENUS PITUOPHIS By Olive Griffith Stull INTRODUCTION From its wide range and varied habitat, its conspicuous size and pattern, and its abundance the genus Pituophis is popularly one of the best-laiown genera of North American snakes. Throughout most of North America these snakes are familiar — under the name of "bull snakes," "pine snakes," or "gopher snakes" in the United States, in Mexico as the "cencuate" or "alicante," and in Lower California as the "corallilo." Nevertheless, it is doubtful whether any other North American ophidian genus is in greater confusion with reference to the taxonomic position of the included forms, and our knowledge of their probable afl&nities. An understanding of the phylogenetic relationships within a genus can be attained only by a synthetic survey of all the included forms, based upon a detailed analytical study of the structural variations of each form in their relation to geograpliic distribution. No such con-sideration of the genus as a whole has been undertaken. The work of Van Denburgh and Slevin (Van Denburgh and Slevin, 1919, and Van Denburgh, 1920) represents the only attempt to correlate varia-tion with distribution, as a basis for the interpretation of affinities between several forms of the genus. The deficiencies that must be recognized in their conclusions are undoubtedly due to the insufiiciency of the material studied and to the limitations imposed by the considera-tion of a circumscribed geographic region. The purpose of the present study is to define the taxonomic status of the included forms on a structural and geographic basis, to deter-mine their mutual affinities as far as is possible from the available material, and to assemble the accumulated data concernmg them. In the attempt to make the conclusions as complete and accurate as possible, material has been borrowed from every available source. In every specimen the scale and pattern features were examined in detail. For every form the teeth were studied in a representative series of specimens, and the hemipenes were dissected in several individuals. Drawings to represent the color pattern of each form have been made from typical specimens. 1
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