X LIST OF ILLUSTRATIONS. 



Page. 

 Fifi. 21. The natural divisions (eiu'ironmental complexes) of the Greater Texas 



Region. (From Hill, Physical Geography of the Texas Region) 60 



22. Distrit)ution of Tharanophis marcianus, as indicated by the locality 



records C2 



23. Habitat of Thamnophis radix and T. sirtalis parietalis. Slough (outlet 



to Elbow Lake), Clay County, Iowa 72 



24. Habitat of Thamnophis radix and T. sirtalis parietalis. Morainic hills 



in Clay County, Iowa 74 



25. Distribution of Thamnophis radix, as indicated hj the locality records. 81 



26. Diagram showing the variation in the dorsal scale formula in Tham- 



nophis radix 82 



27. Diagram showing the ^'ariation in the number of supralabials in Tham- 



nophis radix 83 



28. Diagram showing the variation in the numl^er of infralabials in Tham- 



nophis radix 83 



29. Habitat of Thamnophis butleri. Creek at Lima Center. Washtenaw 



County, Michigan 89 



30. Distributionof Thamnophis butleri, as indicated by the locality records. 93 



31. Diagram showing the variation in the dorsal scale formula in Tham- 



nophis liutleri 94 



32. Diagi'am showing the variation in the number of supralal:)ials in Tham- 



nophis Initleri 95 



33. Diagram sliowing the variation in the number of infralaljials in Tham- 



nophis l>utleri 95 



34. Phylogenetic development of the Radix group 97 



35. Distribution of Thamnophis sauritus proximus, as indicated by the 



locality records 101 



36. Diagram showing the variation in the number of supralaljials in Tham- 



nophis sauritus proximus 102 



37. Diagram showing the variation in the number of ventral scutes in 



Thamnophis sauritus proximus 103 



38. Diagram showing the variation in the proportionate tail length in 



Thamnophis sauritus proximus 104 



39. Diagram showing the variation in the number of subcaudal scutes in 



Thamnophis sauritus proximus 105 



40. Distribution of Thamnophis sauritus sackeni, as indicated by the 



locality records • 109 



41. Diagram showing the variation in the numl^er of supralabials in Tham- 



nophis sauritus sackeni 109 



42. Diagram showing the variation in the number of ventral scutes in 



Thanuiophis sauritus sackeni 110 



43. Diagram showing the variation in the proportionate tail length in 



Thanuiophis sauritus sackeni 110 



44. Diagram showing the variation in the number of subcaudal scutes in 



Thamnophis sauritus sackeni ] 11 



45. Distril)ution of Thamnophis sauritus, as indicated l>y the locality 



records 114 



46. Diagram showing the variation in the numlicr of supralal)ials in Tham- 



nophis sauritus 115 



47. Diagram showing the variation in the numl)er of infralabials in Tham- 



nophis sauritus 115 



48. Diagram sliowing the- variation in the numl)er of ventral scutes in 



Thamnophis sauritus 116 



