Cross bands irregular and usually with a light U-shaped area on each 

 side; belly mostly dark, with sharply contrasting light areas; Texas 

 Aghistrodon mo\eson pictigaster Gloyd and Conant 

 Texas Copperhead 



19. Top of head between and a little behind the area of the eyeballs with 



about three large plates Pigmy Rattlesnakes 20. 



Top of head between the area of the eyeballs with many small scales 



Larger Rattlesnakes 24. 



20. Looking at the head from the side, with one plate above the pit and 



before the eye; usually with a light stripe from below the middle of 

 the eye to the corner of the mouth 2L 



With two plates, one above the other, above the pit and before the eye; 

 usually with a light stripe from below the front of the eye to the 

 corner of the mouth 23. 



2L With about 25 rows of dorsal scales; ground color very dark; Fla. to 

 Miss. 



Sistrurus miliarius harhonri Gloyd Florida Ground Rattler 

 With about 21 rows of dorsal scales; ground color gray or brown 22. 



22. With about 30 dark, mid-dorsal blotches; Mo. to Texas, also to Tenn. 



and Miss. 



Sistrurus miliarius strec\eri Gloyd Western Ground Rattler 

 With over 35 dark, mid-dorsal blotches; N. C. to Ala. 



Sistrurus miUarius miliarius (Linn.) Eastern Ground Rattler 



23. Belly mostly dark; N. Y. to Minn, and Kansas 



Sistrurus catenatus catenatus (Raf.) Eastern Massasauga 

 Belly mostly light; Neb. to Ariz, and Texas 



Sistrurus catenatus edwardsii (B. 6? G.) Western Massasauga 



24. With a conspicuous spine or horn above each eye; Utah to Ariz, and 



Cal. 



Crotalus cerastes Hallowell Horned Rattler, Sidewinder 

 No spine or horn above each eye 25. 



25. With tvv'o large plates, about the size of the eyes, occupying the entire 



transverse area on top of the snout between the front corners of the 

 eyes; tail usually dark; Ariz, to Texas 



Crotalus molossus molossus (B. ^ G.) Black-tailed or Dog-faced 

 Rattlesnake 

 With several small scales or plates in this region; tail banded or striped 

 except in one species, which may have a dark tail 26. 



26. Looking at the head from the front, with the single large plate at the 



end of the snout (rostrum) separated from the large plate before each 

 nostril by small scales; color whitish, dark dotted; Nev. to Ariz, and 

 Cal. 



Crotalus mitchellii pyrrhus (Cope) White Rattlesnake 

 With the rostral plate in contact on each side with the large plate before 

 each nostril; color dark or pale 27. 



27. End of snout sharply keeled; usually with an upright light bar on the 



rostrum; end of tail lengthwise striped; Ariz. 



Crotalus willardi Meek White-banded Rattlesnake 



393 



