13. COLVBRIDJS 



eee. — Rostral very large, with free lateral edges j 

 coloration in spots, and blotches. 



Phyllorhynchus. — p. 692. 

 eee". — Rostral normal, without free edges j colora- 

 tion in blotches, 

 fff. — Gastrosteges fewer than 200. 



Hypsiglena. — p.779. 

 ffF. — Gastrosteges more than 200. 



Trimorphodon. — p. 884. 

 b'. — Anal plate single, 

 cc. — Urosteges in one series (at least anteriorly). Snout 

 protruding^ coloration in cross-bands. 



Rhinocheilus. — p. 773. 

 cc'. — Urosteges in two series. 



ddd. — Scales in 21 to 23 rows; loreal nearly as high 

 as long; rostral not protruding; coloration in 

 rings, blotches, or lines. 



Lampropeltis. — p. 740. 

 ddd'. — Scales in 27 to 31 rows; loreal elongate; 

 rostral prominent; coloration in blotches. 

 Arizona. — p. 701. 

 ,'. — Dorsal scales keeled. Laterals keeled or smooth; 



urosteges in two series. 

 bb. — Anal plate single, 

 ccc. — Prefrontals normally four (often two); scales in 

 27 to 35 rows, several of the lower usually smooth; 

 no longitudinal lines. 



Pituophis. — p.70S. 

 ccc'. — Prefrontals two; scales in 17 to 23 rows; not more 

 than three smooth; usually with longitudinal 

 lines, sometimes spotted or unicolor. 



Thamnophis. — p. 787. 

 bb*. — Anal plate divided, 

 cccc, — Pupil round; rostral not free at edges. 



