30 BULLETIN 61, UNITED STATES NATIONAL MUSEUM. 



noticeably smaller. In such specimens when the formula is 8/9, the 

 reduced tliird superior scute (as in the case of the reduced fourth in 

 the formula 9/10) has not a corresponding inferior labial, but is included 

 within the limits of the preceding inferior scute, which also underlies 

 the second supralabial. Here again is a loss of an inferior labial 

 scute corresponding in position to a reduced superior labial. 



As already seen, it is the reduced third supralabial that is lost to 

 make 7 upper labials, and in the specimens with the formula 7/9 the 

 disposition of the inferior plates in front of the eye is exactly as in the 

 formula 8/10, except that the inferior labial corresponding to the third 

 supralabial in the 8/10 specimens is lacking (fig.7), and likewise the 

 same as in 9/1 1 specimens, except for the loss of the fourth superior and 

 its corresponding inferior scute. In specimens with the formula 7/10 

 (fig. 9), a fourth infralabial is present, but with the third lies entirely 

 under the second supralabial, while in 7/11 a third, fourth, and fifth 

 may be seen beneath the second supralabial. 



Up to this point the reduction in the number of inferior labials, as 

 in the case of the upper labials, has taken place in front of the eye. 

 When the labial formula is 7/9, however, and the penultimate superior 

 labial is narrowed, there is likewise a reduction in the width of the 

 penultimate scute in the inferior series. When the small penultimate 

 supralabial has disappeared, leaving 6, an infralabial scute also tends 

 to disappear, leaving 8, and the same arrangement as in 7/9 specimens 

 is attained, i. e., each superior labial except two are situated above an 

 infralabial (fig. 10); but in this instance it is the first and penulti- 

 mate supralabials which have two corresponding inferior scutes, 

 instead of the first and antepenultimate, as in other instances. In 

 this instance, however, it frequently does not appear that the lost 

 inferior labial is the one corresponding in position to the lost supra- 

 labial, for in many 7/9 specimens in which the penultimate supra- 

 labial is reduced in size the penultimate inferior labial extends partly 

 under the antepenultimate superior scute, thus occupying the place 

 of the posterior small inferior labial that usually underlies this scute 

 and with which it has evidently fused. The penultimate infralabial is, 

 however, first reduced in size at the same time that the corresponding 

 supralabial is pushed forward in the process of reduction, so that it 

 may be considered as the one that is lost in the reduction in the number 

 of infralabials from 9 to 8. 



The reduction in the number of lower labial scutes in the garter- 

 snaTces thus talces jdoA^e in exactly the same manner and at about the same 

 time and place as the decrease in the number of superior labials, which 

 explains the existing correlation in the number of plates in the two series. 

 Examining the diagram (fig. 3) as a whole, it may be seen (1) that 

 the reduction in the two series takes place at about the same time 

 and place, and in the following order from the maximum number: 



