198 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Seh. 



Scale counts in Thamnophis sirlalis concinnus — Continued 



Remarks. — While a dark style of coloration with a tendency 

 toward narrow lines is characteristic of this subspecies, this 

 type of coloration is by no means constant. Specimens similar 

 in color to the type of pickermgii seem to be very rare even in 

 the far north. In general, the difference from T. s. parietalis 

 and T. s. infernalis lies in an increase in the dark pigment, both 

 dorsally and ventrally, rather than in a marked narrowing of 

 the lines or a reduction in the amount of red in the coloration. 

 Some specimens from Oregon are no darker than Californian 

 T. s. infernalis, and show red heads and often much red on the 

 body. Others are quite dark. Upon the whole, and notwith- 

 standing wide individual variation everywhere, it may be said 

 that the coloration becomes lighter toward the south and is 

 gradually changed to that of T. s. infernalis. This color change 

 seems to occur more rapidly (i. e., farther north) than the 

 change in number of gastrosteges. The latter change has been 

 discussed under the heading The Sirtalis Group. 



Thamnophis sirtalis infernalis (Blainville) 



Pacific Garter-Snake. 



Diagnosis. — Gastrosteges and urosteges average more nu- 

 merous than in T. s. parietalis and T. s. concinnus. Coloration 

 usually lighter, with broader lines and more red than in T. s. 

 concinnus, similar to that of T. s. parietalis. 



