SNAKES OF THE GENUS PITUOPHIS 



105 



23 31 46 37 30 25 



azygos, and the rostral penetrating one-half of the distance between 

 the internasals. The dorsal scale formula is 27-33-23, there are 42 

 ventrals on the right neck and 31 on the left before the point of union, 

 and 175 from there to the anal plate. The caudals number 62. The 

 right head also has two more spots in the dorsal series before the 

 junction of the two necks, the total number being 53 or 55 on the 

 body and 16 on the tail. Of this same specimen Johnson (1901, p. 

 526) says: "This specimen is re- 

 markable for the extreme length 

 of the anterior doubled portion, 

 which is much longer than in any 

 case ever described, with the excep- 

 tion of that of Redi. The skia- 

 graph reveals the division of the 

 vertebral column very much far- 

 ther back than that of the bodies 

 proper, although the color mark- 

 ings show irregularities over the 

 portion underlaid by the two ver- 

 tebral columns." 



Another 2-headed specimen, in 

 which, however, the head scales are 

 similar, is described by Pope (1925, 

 p. 161) as follows: "The cephalic 

 plates are similar in number and 

 arrangement and there is a small 

 anterior frontal plate between the 

 four prefrontals and the frontal 

 plate. . . . Our specimen of Bull 

 Snake has the two heads joined 

 together just behind the angle of 

 the jaw, there being one fold of 

 skin connecting the lower jaws 

 for one-half of their length and 

 another fold running diagonally 

 from the angle of one to the 

 posterior base of the skull of the 

 other. Where the vertebrae unite 

 to form a single vertebral column is probably within one inch of their 

 heads." 



Range. — This form has the greatest range of any in the genus and 

 is found throughout the Great Plains region. It occurs from the 

 northern part of Mexico north to Door County, Wis., in the east, 

 and to Medicine Hat, Alberta, Canada, in the west, and ranges from 

 the Rocky Mountains to western Indiana. 



86 



84 



82 



80 



78 



76 



74 



72 



70 



68 



66 



64 



62 



60 



58 



56 



54 



52 



50 



48 



46 



44 



42 



40 



Rej^ion 



No. 



FiQUBE 57.— Geographic variation in total number 

 of dorsal spots in Pituophis sayi sayi. 



