86 



BULLETIN 17 5, UNITED STATES NATIONAL MUSEUM 



Although the number of scale rows tends in general to increase 

 slightly from north to south (fig. 43) and the number of ventrals shows 

 a slight constant increase from California to the extreme southern tip 

 of Lower California (fig. 44), these, as well as the other scale characters, 

 appear to be remarkably constant throughout the range of the species 

 (figs. 45 to 47). For most characters the extremes of variation for the 

 peripheral geographic groups vary but little, if any, beyond the 

 extremes for the area represented by the largest number of specimens 

 and showing the widest range of variation for most of the characters. 

 A larger number of specimens may, of course, greatly extend the 



35-35-25 

 53-35-23 

 32-35-25 

 31-35-24 

 31-35-23 

 32-33-24 

 31-33-25 

 31-33-23 

 29-33-23 

 29-33-21 

 31-31-23 

 29-31-23 



Region No. 1 2 3 4 5 6 V 



FiQUEE 43.— Geographic variation in number of scale rows in Pituophis vertebraltt. 



extremes of variation for those localities. The most marked variation 

 is in the proportionate tail length, which drops gradually from an 

 average of 0.141 in the California specimens to an average of 0.124 in 

 specunens from the Cape (fig. 48). In the number of spots (fig. 49) 

 the only significant variation seems to be in the Cerros Island speci- 

 mens, which have 64 to 81 spots on body and tail (average 68.8), 

 while of all the other specimens examined only two (one from Mira- 

 flores with 61 and one from Trinidad with 73) have more than 60 

 spots on the body and tail. The Cerros Island examples thus form 

 a local race, which I have hesitated to separate from the mainland 

 form because of the very small number of specimens, and the over- 

 lapping, however slight, that exists between the Cerros Island and the 



