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. 



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