188 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



It will be seen that while the average count in males from 

 Washington is 245.5, the average in males from central and 

 southern California ranges from 255 to 265 ; the extremes of 

 variation in the latter area being 251 and 270, while in Wash- 

 ington specimens they are only 239 and 250. Similar differ- 

 ences are found in the counts of female specimens, the Wash- 

 ington average being 230.1, as against central and southern 

 California averages of from 243.7 to 248. Intermediate locali- 

 ties show some intennediate counts, but in general it may be 

 seen that the difference is quite great and constant enough to 

 serve well for the separation of a southwestern race, T. sirtalis 

 inf emails, from the northern subspecies, T. sirtalis coucinmis. 

 This difference in gastrosteges is clearly shown in Figure 1. It 

 also is evident that T. sirtalis concinnus is not confined to the 

 extreme northwest, but, on the contrary, occupies a strip close 

 to the coast south nearly or quite to San Francisco Bay. In 

 the extreme north T. sirtalis concinnus ranges east far from the 

 coast, for the specimens from northern Idaho are of this dark 

 race and it very possibly may be that Cope's type of trilineata 

 from Fort Benton, Montana, also belongs here. A little farther 

 south, however, concinnus does not range far from the ocean, 

 as is shown by the specimens from Klamath County, Oregon, 

 and Modoc County, California, which represent the race T. 

 sirtalis infernalis. 



Thamnophis sirtalis parietalis agrees with T. sirtalis concin- 

 nus in having a smaller number of ventral plates than is to be 

 found in T. sirtalis infernalis. It differs from T. s. concinnus 

 and resembles T. s. infernalis in its lighter style of coloration. 

 Specimens at hand do not show where Thamnophis sirtalis 

 parietalis meets the other two subspecies, or whether there are 

 definite areas of intergradation between these forms. One 

 would expect to find such a state of affairs in Nevada, southern 

 Idaho, and perhaps in southeastern Oregon, but, unfortunately, 

 our specimens from these areas are very few. The Idaho 

 snakes are of the dark T. s. concinnus type, while tliose from 

 Utah are definitely T. s. parietalis. 



We thus recognize from the territory west of the Rocky 

 Mountains three subspecies of Thamnophis sirtalis, as fol- 

 lows : — 



