VARIATIONS OF OARTER-SNAKES. 39 



shape of tlie frontal (i. e., length in relation to width) is also useless 

 as a diagnostic character, owing to its variability; while, as shown 

 above, the position of the eye relative to the supralabials (i. e., the 

 particular labials which enter the orbit), is dependent upon the 

 number of labials in this series. 



THE FOUR GROUPS OF GARTER-SNAKES. 



It may seem the extreme of 'Mumping," in view of the thirty 

 forms *=" that are at present recognized by herpetologists, to assert 

 that there are but four great groups or lines of ctescent in the garter- 

 snakes, but I believe that the evidence is sufficient to warrant the 

 assertion. The first step in the division of the genus into genetic 

 groups is to determine the different associations of traits, or forms, 

 that exist at the present time. This has of course alread}^ been 

 largely accomplished in the definition of the species and varieties 

 that have been made, and it remains for us now to assemble these 

 forms into the general groups.'' 



The table that follows expresses all of the different combinations of 

 characters that are shown by these snakes at the present time, and it 

 will be seen that there are nineteen of these combinations or forms rec- 

 ognized. These comprise all of the different forms of garter-snakes 

 that have a geographic range, and disposes of the multitude of forms 

 that have been described upon the basis of individual or sexual 

 variations. 



« This number has been attained by adding the better defined Mexican and Central 

 American forms to the North American forms admitted by Brown (1901) in his 

 "Review of the Genera and Species of American Snakes North of Mexico" (a con- 

 servative estimate). 



bit is best at theoutstart to ignore all questions of species and subspecies until their 

 status is established, and to speak of these as forms. Forms, therefore, in the sense 

 employed in this paper, are actual combinations of traits, having geographic extent, 

 irrespective of whether they are isolated (species) or intergrade with their neighbors 

 (subspecies). Detailed discussions of questions of nomenclature are also omitted, 

 although the names used are in every case the ones that, in the light of the develop- 

 ment of these investigations, we judge to be the right ones, following the Interna- 

 tional Code of Zoological Nomenclature. The proper name of each form will be 

 found in the footnotes, together with the synonymy. 



