SNAKES OF THE GENUS PITUOPHIS 145 



Variation. — Some geographic variation seems to exist, as may be 

 illustrated by the accompanying graphs. On all the graphs region 1 

 represents Santa Cruz Island, which is graphed as a separate unit, 

 since an island fauna obviously cannot be inserted at any given point 

 in a continuous series of mainland specimens arranged geographically. 

 In the graphs representing the variation in scale characters and in 

 proportionate tail length the numbers 2 to 10 refer to regions in a con- 

 tinuous series from south to north as follows: 



Region 2. San Diego and Los Angeles Counties, Calif. 



3. Kern and San Luis Obispo Counties, Calif. 



4. Tulare, Kings, Fresno, San Benito, and Monterey Counties, Calif. 



5. Santa Cruz, San Mateo, San Francisco, Santa Clara, Merced, Madera, 



Mariposa, Stanislaus, San Joaquin, Alameda, and Contra Costa 

 Counties, Calif. 



6. Marin, Sonoma, Napa, Solano, Eldorado, and Placer Counties, Calif. 



7. Yolo, Sutter, Butte, Glenn, Lake, Mendocino, and Tehama Counties 



and the southern parts of Trinity and Humboldt Counties, Calif. 



8. The northern part of Humboldt County, and Shasta, Modoc, Siskiyou, 



and Del Norte Counties, Calif. 



9. Oregon. 



10. Washington. 



In the graphs illustrating the variation in the numbers of spots these 

 regions have been further subdivided so as to separate the specimens 

 of the coastal strip of California from those of the inland counties. The 

 regions represented are as follows: 



Region 2. San Diego and Los Angeles Counties, Calif. 



3. Kern and San Luis Obispo Counties, Calif. 



4. San Benito and Monterey Counties, Calif. 



5. Tulare, Kings, Fresno, Merced, Madera, Mariposa, Stanislaus, and 



eastern San Joaquin Counties, Calif. 



6. Santa Cruz, San Mateo, San Francisco, Santa Clara, Alameda, Contra 



Costa, and western San Joaquin Counties, Calif. 



7. Eldorado and Placer Counties, Calif. 



8. Marin, Solano, Napa, and Sonoma Counties, Calif. 



9. Yolo, Sutter, Butte, and Tehama Counties, Calif. 



10. Glenn, Lake, Mendocino, Trinity, and Humboldt Counties, Calif. 



11. Shasta, Modoc, Siskiyou, and Del Norte Counties, Calif. 



12. Oregon. 



13. Washington. 



In range of variation the number of scale rows is remarkably con- 

 stant throughout the geographic range of the form, but in the average 

 number there is an evident decrease from south to north (fig. 65). 

 The numbers of ventrals and caudals (figs. 66 and 67) also remain 

 remarkably constant throughout the range, except that there is a 

 marked decrease in the number of caudals in the Oregon and partic- 

 ularly the Washington specimens and that the number of ventrals 

 in the Santa Cruz Island specimens is noticeably low. The latter 

 variation, however, may not represent the true condition of the island 



