SNAKES OF THE GENUS PITUOPHIS 19 



great. For the genus as a whole the range of variation in the number 

 of supralabials is 7 to 10, of infralabials 9 to 15, of preoculars 1 to 

 3, and of postoculars 2 to 6. In several of the forms represented by 

 large series of specimens, such as affinis, sayi, catenifer, and deserticola, 

 the range of variation in several of or all these characters is the same 

 as for the entire genus. In the more specialized forms, such as the 

 subspecies of melanoleucus and the three forms of the deppei group, 

 the variations seem to be more specific, but it must be noted that 

 in all these the series of specimens are too small to furnish conclusive 

 evidence. It is obvious, however, that in each form each of these 

 characters varies around a definite norm. For example, the number 

 of supralabials occurring most commonly is 8 in every form except 

 vertebralis, where 9 is the usual number. The number of infralabials 

 is most often 12 or 13, except in ruthveni and mugitus, where it is 

 commonly 14, and in deppei, where it is commonly 11. Similarly, the 

 number of preoculars is rarely or never more than one in the forms 

 of the deppei group and in the four subspecies of melanoleucus, and 

 is most commonly one in sayi and affinis, while in vertebralis and the 

 three subspecies of catenijer it is usually 2. In most of the forms 

 the most usual number of postoculars is 3, with 4 next in frequency, 

 and in some forms equally common, but in deppei and lineaticollis 

 the usual number is 2, and in jani 3, with 2 occurring more fre- 

 quently than 4. These tliree forms also differ from the rest of the 

 genus in the entrance of two supralabials into the orbit, instead of 

 one. These are usually the fourth and fifth, but are occasionally 

 the third and fourth (when the number of supralabials is 7), or the 

 fifth and sixth (when the number of supralabials is 9). 



No fixed rule as to the method of reduction in the number of 

 labials can be discovered. Indeed, specimens are not infrequently 

 found in which the number of labials is the same on both sides of 

 the head, but obviously results from the fusion of different scales on 

 either side. In one specimen of m. melanoleucus, for example, with 

 7 supralabials on either side, the fusion of the second and third has 

 apparently occurred on the right side, while on the left side the 

 fifth and sixth have evidently been fused. Blanchard's general rule 

 for change in the number of labials in Lampropeltis (1921a, p. 14) 

 apparently has no application to either supralabials or infralabials 

 in Pituophis. It reads: "In reduction — when the number of labials 

 is odd a scute is lost behind, and when the number is even, one is lost 

 in front of the eye; in addition — when the number of labials is odd, 

 a scute is added in front of the eye, and when the number is even, a 

 scute is added behind the eye." In the change from 8 to 9 supra- 

 labials a scale is usually added in front of the eye, but the change 

 from 9 to 10 and from 7 to 8 may residt from the addition of a scale 

 either behind or in front of the eye. The changes in the infralabials 



