130 



4. Anal plate divided. 5. 

 Anal plate not divided. 17. 



5. Dorsal scales keeled more or less. 6. 

 Dorsal scales not keeled. 15. 



6. Nostril between two nasal plates. 7. 

 Nasal single, pierced by nostril. 14. 



7. Prefrontals two. 8. 



Prefrontal single. No. 3. Haldca xtriatula. (L..) Plate XV. 



8. Loral plate present. 9. 

 Loral plate absent. 13. 



9. Scales on back and sides all keeled. 10. 

 Scales on sides not all keeled. 12. 



10. Scales 19 to 21 rows. 



Scales in 23 rows. No. 11. Natrix sipedon (L.) Page 152. 



11. Without yellow lateral stripe; lower row of scales smooth. No. 9. Reyinia 



rigida (Say). Page 150. 

 With yellow lateral stripe; Scales all keeled. No. 10. Rtginia leheiis (L.) 

 Page 150. 



12. Scales in 27 rows. No. 12. Callopcltis ohsoletus (Say). Page 157. 

 Scales in 25 rows. No. 13. CallopeUis vulpiiius (B. & G.) Page 161. 



13. Scales in 15 rows. No. 4. Stoicria occipitomacuUtta. (Storer). Page 136. 

 Scales in 17 rows. No. 5. Sloreria dekayi (Holbr.) Page 138. 



14. Scales in 19 rows. No. 6. Clunophis kirtlandi (Kenn). Page 140. 

 Scales in 17 rows. No. 14. OpltMdrys aestivus (L.) Page 162. 



15. Nasal single. No. 15. Llopeltis venuiHs (DeKay). Page 164. 

 Nasals two. 16. 



16. Head flat, preoculars equal in size. No. IS. Diadophis piuictatus (L.) Page 171. 

 Head not degressed; upper preocular larger than lower. No. 16. Batcanion 



cunstrictor. (L.) Page 166. 



17. Dorsal scales all or pai't of them keeled. IS. 

 Dorsal scales not keeled. 20. 



18. Scales 29. No. 17. Pituuphvi nielanoleucus (Daudin). Page 171. 

 Scales 19.19. 



19. Lateral stripes on 3rd and 4th I'ows of scales. No. 7. No. 7. TIui»uwphis 



saurita (L.) Page 141. 

 Lateral stripes on 3rd and 4th rows of scales. No. 8. ThanDiophin nirtalis 

 (L.) Page 143. 



20. Ventral plates 210 to 240, chiefly black with yellow lines. No. 19. Lnmpro- 



peltis getulus. (Say). Page 174. 

 Ventral plates 180 to 210, grayish with black borders around brown blotches. 

 No. 20. Lnmpropeltix doliatxiK var. triaiiuulun (Boie). Page 174. 



(For the Key to Ciotalidte or the Venomous Snakes, see page 186). 



(b). SIMPLE STRUCTURAL KEY. 



A. Scales not keeled, or AA. 



B. Anal plate bifid or divided, or BB. 



C. Scales in fewer than 20 rows, or CC. 



D. Scales in 13 rows. No. 1. Ground Snake. Page 134. 

 DD. Scales in 15 to 17 rows. 



E. Ventral plates not as many as 165, or EE. 



F. Ventral plates about 120. No. 2. Valeria's Snake. Page 135. 

 FF. Ventral plates about 140. 



G. Blackish, with yellow collar. No. 18. Ring-necked Snake. Page 171. 

 GG. Green, no collar. No. 15. Grass Snake. Page 164. 



ETC. Ventral plates more than 165, about 185. No. 16. Black Snake. Page 166. 

 CC. Scales in 25 or 27 rows. (Middle scales slightly keeled.) 

 D. Scales in 27 rows. No. 12. Pilot Snake. Page 157. 

 DD. Scales in 25 rows. No. 13. Fox Snake. Page 161. 

 BB. Anal plate entire. 



