SNAKES OF THE GENUS PITUOPHIS 3 



Agriculture and Mechanic Arts; to L. M. Klauber, of the San Diego 

 Society of Natural History ; to Miss Elberta L. Craig, of the University 

 of Colorado; to Dr. Vasco M. Tanner, of Brigham Young University; 

 to Prof. Howard S. Erode, of Wliitman College; to Dr, D. J. Leffing- 

 well, of the Charles R. Conner Museum of the State College of Wash- 

 ington; to W. B. Mabee, of Montana State College; to Dr. H. P. 

 Loding, of the Alabama Museum of Natural History; to Roy E. 

 Rodock, of Lewiston State Normal School; to Prof. John W. Scott, 

 of the University of Wyoming ; to Prof. Franldin Sherman, of Clemson 

 College; to Prof. J. Percy Moore, of the University of Pennsylvania; 

 to Frank C. Baker, of the University of Illinois; to Prof. Austin P. 

 Larrabee, of Yankton College; and to O. B. Giltner, of St. Ambrose 

 College, for the loan of specimens from the collections of the institu- 

 tions they represent. 



I am equally indebted to L. M. Klauber and Percy Viosca, Jr., for the 

 use of their private collections. Mr. Viosca's collection included the 

 type of ruthveni, which has since been deposited in the collection of 

 the United States National Museum. Live specimens were also sent 

 to me by Mr. Klauber, some of them through the kindness of Charles 

 Bogert. 



To Mrs. Helen T. Gaige, the late Dr. Frank N. Blanchard, and 

 Prof. E. C. Case, all of the University of Michigan, I am grateful for 

 advice and criticism. Helpful data were furnished by Dr. Blanchard, 

 M. F. Angel, Dr. C. S. Brimley, Dr. H. S. Brode, Henry W. Fowler, 

 L. M. Klauber, Prof. Franldin Sherman, and Dr. Tracy I. Storer. 



Figures 2 to 5 were drawn on enlargements of photographs, and the 

 photographs subsequently faded. The photographic work was done 

 by Miss Dorothy Chipman, of the Museum of Zoology of the Univer- 

 sity of Michigan, and the drawings, as well as figure 6, were made by 

 Miss Grace Eager, of the same Museum. To both of them I wish 

 to express my gratitude. 



Dr. Norman Hartweg I sincerely thank for much kind assistance 

 in the laboratory, and the tender care of my live specimens during 

 my absence. 



Above all, I am indebted to President Alexander G. Ruthven, of 

 the University of Micliigan. At his suggestion the problem was 

 undertaken, under his direction the work has been carried on, and 

 its completion is due to his unfailing advice and encouragement. To 

 him I dedicate tliis study as an expression of my appreciation. 



NOTES ON THE ILLUSTRATIONS 



On the graphs illustrating sexual variation (figs. 7-9) the numbers 

 on the abscissas represent the characters, while those on the ordinates 

 indicate the frequency. On all other graphs the locahties represented 

 are indicated on the abscissas by name or number. In the latter 



