13. COLUBRID^ 



The color above is uniform light grayish, yellowish, or 

 brownish olive, with more or less distinct blackish markings 

 laterally upon the bases of many of the scales of the fourth 

 and fifth, and sometimes of the first and eighth, rows. The 

 lower surfaces are pale grayish yellow, the tips of the gas- 

 trosteges being tinged with the color of the back. 



A second type of coloration, shown by certain melanistic 

 specimens, has been described (Natrix cel^no) but doubt- 

 less is only an individual variation. In it the ground color 

 both above and below is grayish black. A lighter stripe of 

 bluish gray extends along the side from the neck to the tail. 

 Anteriorly this stripe occupies the second, third, and part of 

 the first, rows of scales, and sometimes shows irregular 

 dorsal expansions or vertical bars separated by interspaces of 

 the blackish ground color about one and a half or two scales 

 wide. Posteriorly the lateral stripe usually becomes darker 

 and more indistinct and may or may not involve the scales 

 of the first row. The lower surfaces are grayish black often 

 marbled with lighter. 



Some specimens are more or less intermediate between 

 the two types of coloration. Some show, more or less dis- 

 tinctly, seven longitudinal stripes, alternating light and dark, 

 from head to tail. 



Length to anus +32 5+0 575 620 682 687 



Length of tail 1+9 163 183 180 208 250 



Distribution. — Natrix valida was first described by 

 Robert Kennicott, in 1860, from a specimen collected in 

 Durango, Mexico. It has since been found in other parts 

 of the Mexican mainland. It probably does not occur in the 

 United States. Professor Cope recorded a specimen (U. S. 

 Nat. Mus. No. 4650) as having been collected in Rabeh 

 Valley, Utah, but recent examination shows that this speci- 

 men is a Thatnno-phis o. vagrans with a divided anal plate. 



