AMPHIBIA AND REPTILIA OF COLORADO 83 



than those in front; small to medium sized snakes; general color 

 pattern of three stripes, a dorsal and two laterals, on a darker ground 

 color. 



The Garter Snakes, genus Thamnophis, are the most abundant 

 and most variable group of North American snakes. The color pat- 

 tern, and the number of scale rows, labials and other plates are sub- 

 ject to great variation, almost every combination within the limits of 

 the genus being known. As a result some sixty-five forms of Tham- 

 nophis have been described, which have been variously ranked by 

 different zoologists as species, varieties and synonyms. The garter 

 snakes are usually semi-aquatic in habit. Few species are found far 

 from water. All species are viviparous and produce large numbers of 

 young. When pursued the garter snakes will try to escape but when 

 captured they attempt to bite vigorously and usually emit a substance 

 from the anal glands which gives off a sweet, sickening odor. These 

 snakes are quite harmless. 



Range, from Central America over most of North America as far 

 north as Canada. 



Key to the Colorado Species of Thamnophis 



It is to be noted that the species of this genus vary in such a way as to produce 

 a seeming intergradation of all forms. Several types are distinct, however, and 

 of these four are found in this state. In the identification of Garter Snakes par- 

 ticular attention should be paid to the locality from which the specimen was 

 collected. 



a. Lateral stripe on the third and fourth rows of scales. 



b. Superior labials, seven; plains species; in Colorado east of the main 

 range Th. radix (Baird and Girard). 



bb. Superior labials, eight; southern Colorado. Th. megalops (Kennicott). 

 aa. Lateral stripe on the secotid and third rows of scales. 



c. Superior labials, seven; dorsal scales in nineteen rows; postgenial a 

 fourth to a half longer than the genial; sides of the body above the 

 lateral stripe with spots of brick red color; Colorado, general. 



Th. parietalis (Say). 

 cc. Superior labials, eight; dorsal scales in twenty-one rows; genials and 

 postgenials subequal; Colorado, general except in the eastern plains. 



Th. elegans (Baird and Girard) . 



