No. 500] NOTES AND LITERATURE 



553 



single genus of snakes, marks a new departure in North Amer- 

 ican herpetology in respect to methods of procedure. An at- 

 tempt is made first to determine the value of the characters 

 commonly employed in distinguishing the different forms of the 

 group, as scutellation and color, through study of the normal 

 range of variation in the number of dorsal rows of scales, num- 

 ber and arrangement of the labial and preocular plates, the 

 number of the ventral and subcaudal plates, and the position 

 and color of the stripes. All this is worked out with great care 

 and detail for each form, so far as material is available, which 

 includes about 3,000 specimens, gathered from throughout the 

 known range of the genus. Distinction is made between indi- 

 vidual, sexual and geographic variation. 



The individual variation in the number of rows of dorsal 

 scales, and the variation in the different forms of the group, is 

 found to be due to the dropping out of certain rows. The law is 

 thus stated: "The individual, geographic and racial variations 

 in the number of dorsal scale rows in the garter-snakes is brought 

 about by the shortening and loss of the same scale rows as are 

 ordinarily dropped posteriorly in conformity with the taper of 

 the body, and there is evidence that this decrease is due to a 

 dwarfing of the body." 



The cause of variation in the number of labial plates is not 

 easily explained, but it is believed that there is good reason "for 

 concluding that whatever the factors may be that influence the 

 number of labial plates, the variations arc <rt 'O Lira phi c and have 

 been the basis for the racial differences that now exist. ' ' 



The color pattern in Thamnophis consists of three light longi- 

 tudinal stripes — a median, and a lateral stripe on each side of 

 the body — on a dark ground. They vary in width in different 

 individuals of the same form, and also more or less in color. The 

 median stripe is the most variable, and in some of the forms 

 it is more or less obsolete. The lateral stripes are constant in 

 position (in reference to the rows of scales involved), and as the 

 position varies in different groups of forms it is available in 

 diagnosis. Simple variation in color, however, has little diag- 

 nostic significance, owing to the wide range of individual varia- 

 tion within each form; "and, even when there are well marked 

 geographic differences among forms, those in the same region 

 tend to be similarly colored, as Allen has pointed out a number 

 of times in mammals and birds, so that it is impossible to dis- 



