NO. 2179. VARIATION IN GARTER SNAKES— THOMPSON. 351 



Diagram showing the variation in the number of gastrosteges in specimens Jrom San 



Francisco. 



9 S <^ 



9 c? <? 



9 c? 9 9 9 <? c? 



9c?9 99<5'(?99 



999999c?d'c?<?c? c? 



9 99999^9c?9c?c?c?c?<? 9 



147 14S 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 



Females. 



Males. __^__^^ 



Ransje of variation in 50 specimens 147-166 



Males, 23 specimens 152-162 



Females, 27 specimens 147-166 



Diagram showing the variation in the number of gastrosteges in Sausalito specimens. 



$ 



9 c? 9 c? 



9 c? <? c? c? 



9 9 c? 9 <? (? 



9 999crc?9 c?c? 



9 9c?9$c?9(?(?c?c?Jc? c?(? 



959 9999^c?c?d^d'9cf<?9c?c?c? 



145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 



Female. 



Male. 



Range of variations in 59 specimens 145-164 



Males, 34 specimens 150-164 



Female, 25 specimens 145-161 



An occasional specimen is seen in which some of the gastrosteges 

 are incomplete in that they fail to reach across the body. These m- 

 complete shields usually extend nearly to the median line. Where 

 there are several on one side the asymmetry is often compensated 

 for by there being nearly an equal number on the opposite half of the 

 body. 



One specimen, a female, from San Francisco, Cat. No. 53574, 

 U.S.N.M. (Orig. No. T-136), that is not included in the series, has 

 nine incomplete gastrosteges on the right and none on the left side of 

 the body. It is further abnormal in having a low gastrostege count 

 of 149 (right), a scale formula of 21—19—17—15, and eight infralabial 

 shields on the left side. 



Variation in Anal. 



The normal condition is for this shield to be entire. There are no 

 specimens in this series in which it is divided. 

 Variation in Urosteges. 



These plates are normally paired. An occasional specimen may be 

 found in which from one to two of the urosteges remain entire. When 

 this occurs, these undivided shields are regularly situated near the 

 base of the tail. All showing this variation are males. 



Paired throughout, 94 per cent; 1 to 2 entire, 6 per cent. 



