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BULLETIN 17 5, UNITED STATES NATIONAL MUSEUM 



slight, or, on the other hand, a wide range of individual or sexual varia- 

 tion may be present throughout the range of the form, and neverthe- 

 less show only a slight correlation with geographic distribution, or 

 none at all. In the attempt to determine the relative value of scale 

 and pattern characters in indicating relationships, the relative con- 

 stancy of a character throughout the group is the best index to its 

 diagnostic importance. 



In the genus Pituophis the amount of individual variation is very 

 great, and completely overshadows the geographic variations, which, 

 though in most forms slight, are nevertheless observable in many of 

 the characters. The apparent insignificance of the geographic 



50-4 55-9 60-4 65-9 70-4 75-9 



Figure 8.— Sexual variation in the number of caudals in 72 specimens of Pituophis c. catenifer from the 



vicinity of Palo Alto, Calif. 



variation may be due in some cases to the small amount of material 

 available, but it seems probable that if a marked variation were 

 present it would be evident in even a small series of specimens. 

 Even in the case of sayi, with the largest range of any form of the 

 genus (extending from Mexico to Canada, and from Colorado, 

 Wyoming, and Montana to Indiana) and a large series of specimens 

 fairly representative of the entire range of the form, the individual 

 variation that exists shows only a moderate correlation with the 

 distribution. In other forms a correlation is generally less rather 

 than more evident. Graphs illustrating the geographic variation in 

 scale and pattern characters are included in the discussion of the 



