108 Zoology of Colorado 



present in the other species, which represents the restricted sub- 

 genus Uta. 



Our snakes are readily divided into the venomous Crotalidae, 

 or rattlesnakes, and the harmless (indeed, beneficial) Colubridae. 

 In the Massasauga (Sistrurus catenatus edwardsii of Baird and 

 Girard), the general appearance is that of the Prairie Rattlesnake, 

 but the head above has nine large plates, instead of numerous 

 small scales. It is a southern form, obtained by Beardsley in 

 Baca County. The Prairie Rattlesnake (Crotalus confluentus of 

 Say) is our common species. The original specimen, obtained 

 on Long's Expedition, probably came from near the place where 

 Fountain Creek joins the Arkansas. A single specimen of the 

 Western Diamond Rattlesnake (C. atrox of Baird and Girard) has 

 been found at Trinidad. It will be known by the distinct black 

 rings on the tail, and the diamond-shaped areas on the back. 



Our Colubridae include eleven different genera, separated 

 on rather technical characters, but on the whole readily recog- 

 nizable. The small Black-headed Snake (Tantilla nigriceps of 

 Kennicott) is the most distinct, and is said to be somewhat poison- 

 ous, though practically harmless to man. It is yellowish or red- 

 dish with a black head; the dorsal scales smooth and polished, 

 in 15 rows. It has been taken at La Junta and Yuma. The 

 Garter Snakes (Thamnophis) are known by the keeled scales, 

 in 1 7 to 2 1 rows, and entire anal plate. They are the commonest 

 of our snakes, usually found in the vicinity of water. The most 

 abundant one is the Western Garter Snake (T. ordinoides vagrans 

 of Baird and Girard), recognised by the lateral stripe being on 

 the second and third rows of scales, the dorsal scales in 21 rows, 

 and the superior labial scales eight. Related to this, but with 

 dorsal scales in 19 rows, and seven superior labials, is the Red 

 Barred Garter Snake (T. parietalis of Say), discovered on Long's 

 Expedition. It has been found at Boulder, Denver, Fort Collins, 

 Greeley and Julesburg. The other two species have the lateral 

 stripe on the third and fourth rows of scales. The Plains Garter 

 Snake (T. radix of Baird and Girard) has seven superior labials, 

 and is common in the vicinity of Denver and Boulder. The 

 Arizona Garter Snake (T. megalops of Kennicott) was taken at 

 Rio Grande by H. W. Henshaw in 1873, but has not been obtained 

 in Colorado since. It has eight superior labials. Two other 



