Tail usually more than onc'fourth total length; scales along the edge of 

 the upper jaw usually pale; belly usually plain colored 72. 



71. With 21 rows of scales anteriorly; with eight, sometimes nine, upper 



labials; stripes usually greenish; Texas to Cal. 



Thamnophis macrostemma (Kcnnicott) Arizona Garter Snake 

 (Thamnophis megalops (Kennicott) ) 

 With 19 rows of scales anteriorly; with seven, sometimes eight, upper 

 labials; stripes usually bright yellow or orange; 111. and the Great 

 Plains, northwestwards 



Thamnophis radix (B. ^ G.) Plains Garter Snake 



72. Usually with seven upper labials; with three bright yellow stripes on the 



body and usually with a streak of bright yellow before each eye; 

 Maine to Mich., and southward to Ga. 



Thamnophis sauritus saiiritus (Linn.) Ribbon Snake 

 Usually with eight upper labials; with the dorsal stripe noticeably differ' 

 ent from the laterals, either much deeper color or else very faint; with' 

 out a yellow streak before each eye or with only a very dull one 73. 



73. Dorsal stripe conspicuous and brighter than the laterals; Colo, and Neb. 



to Wis., and southwards (See note at end of chapter) 



Thamyiophis sauntus proximus (Say) Western Ribbon Snake 

 Dorsal stripe paler than the laterals, often absent except anteriorly; Fla. 

 to Miss. 



Tham.nophis sauritus sac\enii (Kennicott) Southern Ribbon 

 Snake 



74. With the lateral stripe passing anteriorly through the third row of scales 



only; with a bright yellow crescent on each side of the back of the 

 head; Kansas to Cal. 



Thamnophis marcianus (B. & G.) Marcy's Garter Snake 

 With the lateral stripe passing anteriorly through the second and third 

 rows of scales, or sometimes absent; head color various 75. 



75. Greatest number of rows of scales on the body 21 or 23 (not counting 



the ventral plates) 76. 



With nineteen or less rows of scales 83. 



76. Most of the dorsal stripe present 77. 

 Most of the dorsal stripe absent 80. 



77. Belly brown; lateral stripes obscure; Cal. 



Thamnophis ordinoides g'igas Fitch Giant Garter Snake 

 Belly gray or marked with black; lateral stripes distinct 78. 



78. Dorsal stripe with blurred or spotted edges; belly marked with black 



along the mid-ventral line; Mont, to Ariz., and westwards 



Thamnophis ordinoides vagrans (B. fe? G.) Great Basin Garter 

 Snake 

 Dorsal stripe with sharp edges; belly often clouded with black 79. 



79. Belly pale, with few black markings; usually with one preocular plate 



on each side; southern Pacific States 



Thamnophis ordino-ides elegans (B. ^ G.) Pacific Garter Snake 

 (Eutaenia elegans (B. &? G.) ) 



401 



