SNAKES OF THE GENUS PITUOPHIS 29 



On the tail the spots appear as black bars 2 or 3 scales each in length. 

 The spots number 32 to 44 on the body (average 36.9) and 9 to 16 on 

 the tail (average 12.7). They are black or dark brown anteriorly 

 and posteriorly, and brown, usually outlined with darker brown, in the 

 middle of the body. The ground color in alcoholic specimens is 

 yellowish white or buff, tending in some specimens to be almost orange 

 in the anterior interspaces. In most specimens, in at least the ante- 

 rior region, many of the light scales of the sides and interspaces bear 

 a small central dark spot. The belly is a yellowish white and lacks 

 spots anteriorly, or has small dark spots scattered irregularly at the 

 sides of the ventral scutes. Posteriorly and under the tail there is a 

 series of small dark spots on either side, which are 1 or 2 scutes each in 

 length and are separated by 1 to 4 scutes. Anterior to the vent and 

 on the under side of the taO additional small spots are scattered irre- 

 gularly between the lateral series. The head and throat are usually 

 pale, with dark lines between the supralabials and between the infra- 

 labials, and sometimes with small brownish spots appearing as far 

 anterior as the frontal and supraoculars. (Fig. 11.) 



Variation. — As the number of specimens under consideration in the 

 study of this form is small, the results obtained in attempting to corre- 

 late variation with distribution must be accepted with caution. This 

 is especially true in regard to characters that show a marked sexual 

 variation, as unequal proportions of the sexes from given localities 

 would tend to distort the averages and extremes of variation for those 

 localities. Some geographic variation seems to be evident, however, 

 in several of the characters. 



From southern to northern Mexico, there is a slight tendency 

 toward an increase in the dorsal scale formula, as shown by the graph 

 (fig. 12). This tendency continues to California, but from northern 

 Mexico to Texas there is, on the contrary, a decrease. It must be 

 remembered here, as in the discussion of all other characters of this 

 form, that the data of the Texas and Cahfomia specimens may be 

 very deceptive, as there were in the available collections only two 

 specimens from the former region, and one from the latter, which may 

 in either case represent an extreme of variation for the region in any 

 of or all the characters. The tendency of the ventrals (fig. 13), as 

 well as the caudals (fig. 14), to increase from south to north is negligi- 

 ble. The increase in the Texas specimens, however, is sufficiently 

 marked in both cases to make the sum of ventrals and caudals (fig. 15) 

 in both Texas specimens lie without the range of variation for the other 

 specimens of the series. The only specimen with 7 supralabials is 

 from the southern part of the range, and, although the average number 

 shows a slight decrease from south to north in Mexico, it is apparent 

 from a consideration of both extremes of variation and averages for 

 the entire series that any general trend that may be present is rather 



