COUES AND YAEEOW ON HEEPETOLOGY. 279 



EuTiENiA RADIX TWiNiNGi. Goucs & Yarrow. 

 Twining's Garter Snake. 



Description (No. 1135, Two Forks of Milk Eiver, July 15, 1874).— 

 From the Coteau de Missouri westward, in the arid regiou of the Upper 

 Missouri aud Milk Eivers, the characters of E. radix undergo con- 

 siderable modification. The difference is easily recognized in life by an 

 observer familiar with both kinds. The principal character is seen in 

 the increased breadth and intensity of coloration of the dorsal band, 

 especially on the anterior portion. This band is of a rich chrome-yellow 

 or reddish-golden, contrasting strongly with the clear pale yellow of the 

 lateral stripe. This richly-colored cadmium-yellow band commences as 

 a minute linear trace on the middle borders of the two scales just poste- 

 rior to the occipitals ; it then covers a single scale in rear of these, grad- 

 ually increasing until three or even four scales are covered, finally set- 

 tling down to thin scales which continue down two-thirds of body, then 

 covers one whole and two halves; opposite the anus, and to its termina- 

 tion, it is confined to two half-scales. At its broadest part, near the 

 head, it is full three scales broad, and sometimes even three and two 

 half-scales in width. There are slight or no indications of darker mot- 

 tling, even in the lighter-colored specimens. Below the lateral band, the 

 dark color is usually much broken up with mottling of the color of the 

 belly. With much the same general form as in E. radix, the head ap- 

 pears decidedly narrower and less obtuse. In the specimen 1135 there 

 are eight upper labials on right side, seven on left ; it is a gravid fe- 

 male. 



This form corresponds perfectly with certain geographical faunal 

 areas which are represented in the region under consideration, a fact in 

 further evidence of the propriety of distinguishing it. It is abundant 

 about the prairie pools of the Upper Missouri and Milk Eivers ; its habits 

 are the same as those of jE7. radix. It does not appear to extend into 

 the Saskatchewan watershed. 



Dedicated to Maj. W. J. Twining, United States Engineers, in recog- 

 nition of his cordial cooperation in the scientific interests of the Bound- 

 ary Comniission, and in expression of our personal consideration. 



List of specimens (of both forms). 



