N0.21T9. VARIATION IN GARTER SNAKES— THOMPSON. 



349 



Scale Formula 19—21—19—17—15. 



This is not a common variation. It occm-s in 8 per cent of the 

 series, and of these 50 per cent are males. In specimens with this 

 formula there are five zones on the body, each with a different comit. 

 In two examples the VII rows reappeared just anterior to the vent, 

 thereby increasing the count to 17 in this zone. 



Scale Formula 19—17. 



This formula is found next in frequency to the normal. It occurs 

 in 14 per cent of the series, and of these 86 per cent are males. Two 

 specimens in this table exhibited bilateral symmetry, the rows ter- 

 minating on each side at exactly the same level. 



Scale Formula 



-17—15. 



It occurs m but 6 



This is the least frequent comit m the series, 

 per cent, of which 66 per cent are males. 



In both these specimens the VII rows reappear a short distance 

 anterior to the vent. 



