VARIATIONS OF GARTER-SNAKES. 29 



result of the narrowing and final loss of the fourth, third, and eighth 

 scutes consecutively, as numbered on a snake with 9 plates in this series. 



I have previously noted that the number of labials in the upper 

 and lower series is correlated, and that a reduction in the supra- 

 labials is associated with a decrease in the number of infralabials. 

 The method of reduction in the number of the inferior labials is, how- 

 ever, somewhat more obscure, for, owing to the small size of these 

 plates, it is often difficult to detect any decrease in the size of indi- 

 vidual scutes, so that in forms with a different number of scutes in 

 the lower series it is very difficult to say just wliich plates have been 

 lost. Much light can be thrown upon the prol)lem, however, by cor- 

 relating the position of the individual plates of the two series." If a 

 specimen of megalops with the labial formula 9/11 be examined it 

 may be noted that the upper margin of each individual scute in the 

 lower series corresponds almost exactly in width and position to one 

 in the upper series, except that the first and seventh supralabials are 

 above two scutes in the lower series. This arrangement is quite 

 accurately maintained in all of the specimens with this formula exam- 

 ined. If, however, a specimen with the labial formula 9/10 be scru- 

 tinized it will be found that, wliile the same arrangement is for the 

 most part adhered to, the small fourth labial has not in these speci- 

 mens a corresponding infralabial, but that the precetling infralabial 

 scute (the fourth) extends backward to the posterior margin of the 

 fourth supralabial (fig. 5). Evidently, then, either the third or 

 the fourth infralabials are not present in these specimens, or they 

 have fused into a single scute. Just wliich method prevails is imma- 

 terial, for we hope to show that in other cases, as well as in tliis one, 

 the reduction in infralabials always takes place beneath the upper 

 labial scute that is being reduced ; and as was seen in the case of the 

 upper labials that the upper scute is first reduced and finally fused, 

 it may be taken for granted that it is the corresponding infralabial 

 that is lost. 



In specimens with the labial formula 8/10 the third superior has a 

 single corresponding inferior labial scute (fig. 4), and there is in such 

 specimens a condition exactly similar to 9/11 forms, except that the 

 fourth supralabial and its corresponding infralabial (the fifth) are lost. 

 In those rather rare cases where the formula 8/11 is shown, it is inter- 

 esting to note that there are two infralabials below the third supra- 

 labial, so that the arrangement is exactly similar in 9/1 1 forms except 

 that the fourth supralabial only has disappeared. 



In the specimens that show a tendency toward a reduction in the 

 labial formula below 8/10 the third superior, as already noted, becomes 



" The points brought out in the following discussion are illustrated in the diagram 

 (fig. 3). 



