84 UNIVERSITY OF COLORADO STUDIES 



Thamnophis radix (Baird and Girard) 

 Plains Garter Snake (Figures 17, 18 and 20) 



Eulainia radix Baird and Girard, Cat. N. Am. Reptiles, Pt. I, p. 34, 1853. 



Eutaenia marciana — Yarrow, Wheeler Survey, Vol. V, p. 555, 1875 (Pueblo, 

 Colo.); Yarrow, U.S.N.M. Bull. 24, p. 118, 1882 (Pueblo, Colo.). 



Eutaenia radix — Cope, Repl. U.S.N.M., p. 1028, 1898 (Pueblo, Colo.); 

 Ruthven, U.S.N.M. Bull. 61, p. 77, 1908 (Pueblo, Greeley, Ft. Collins, Colo.). 



Dorsal scales typically in 21 rows, in 19 or 21 rows just back of the 

 head, and in 19 or rarely 17 rows over the posterior portion of the 

 body; first row of scales faintly, if at all, keeled, others distinctly 

 keeled, especially those in the mid-dorsal region. Superior labials, 

 usually 7, 1st, 2d, 3d and 7th subequal, 4th, 5th and 6th larger, the 

 5th being the largest; inferior labials, usually 10, 1st longest, directed 

 mesially and posteriorly, so as to meet the 1st from the opposite side 

 in the mid-ventral line, 2d smallest, 6th largest and widest. Ventrals, 

 about 150, 140-180. Tail one-fifth to one-fourth of the total length. 



General color brown or olive, darker dorsally; ventral parts pale 

 yellow, yellowish green or greenish blue. A mid-dorsal stripe, vary- 

 ing in color from a pale lemon yellow to a rich orange red or orange 

 brown, usually orange, beginning in the posterior angle of the parietal 

 plates and continuing to the tip of the tail, covering only one row of 

 scales at its origin, widening over three or four rows just back of the 

 head, narrowing again so as to cover only a single mid-dorsal row and 

 half or more of the adjacent row on each side, from the anal region on, 

 covering only parts of two rows. A lateral stripe of pale yellow, blue 

 or green, somewhat interrupted by black spots from above and below, 

 covering more or less completely the third and fourth rows of scales on 

 each side, beginning just back of the angle of the jaw and continuing 

 to the base of the tail or beyond. Space between the dorsal and 

 lateral stripes dark and in general of a checkerboard pattern, which 

 is formed by two or three rows of black or dark green spots, each 

 covering about three scales, alternating with the lighter ground color. 

 Below the lateral stripe an irregular row of dark spots alternating with 

 patches of the bluish or yellowish ground color. Two small pale 

 yellow spots, often more or less confluent, on the parietals near or 



