XII LIST OF ILLUSTRATIONS. 



Page. 

 Fig. 77. Forests in the Porcupine Mountains, Michigan 177 



78. Distribution of Thamnophis sirtalis, as indicated by the locality records. 180 



79. Variation in the number of supralabials in 113 specimens of Tham- 



nophis sirtalis from southeastern Michigan 182 



80. Variation in the number of infralabials in 113 specimens of Thamnophis 



sirtalis from southeastern Michigan 183 



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



Thamnophis sirtalis 183 



82. Phylogenetic development of the Sirtalis group 186 



