352 Univi rsity of California Publications in Zoology [Vol. 10 



Our ascription of the two forms of gophers to Schain's Ranch 

 is, of course, not in harmony with this view; but our decision 

 may well have been due to incorrect determination of the speci- 

 mens concerned, which are immature; geographic intergradation 

 between ca lx zona* and nigricans is not beyond possibility. 



Thomomys nigricans Rhoads 



Tawny < ropher 



Twenty-four of the gophers taken in the San Jacinto region 

 have, after close comparison, been referred to this form. The 

 localities represented are Schain's Ranch, 4900 feet, four (nos. 

 1625, 1i;l , 7. 1641, 1642); Fuller's Mill, 5900 feet, one (no. 1715); 

 Strawberry Valley, 6000 feet, ten nos. 2139-2148) ; Herael Lake. 

 44IMI feet, live (nos. 2233 2237 ; Thomas .Mountain. 6800 feet. 

 one (no. 2232); Kenworthy, 4500 feet, two (nos. 1862, 1863); 

 and Santa Rosa Peak, 7500 feet, one mo. 1990). It will be noted 

 that these localities lie within a vertical range of 3100 feet (4400 

 to 7500 feet i. also that the life /.one is in each case high Upper 

 Sonoran or Transition, or better expressed, the belt of blending 

 of these two zones. The metropolis of Thomomys nigricans, judg- 

 ing from the results of extensive field work in southern Cali- 

 fornia, as represented by large suites of specimens in the Museum, 

 is a corresponding zonal belt lying along the western slopes of 

 the mountains of San Diego County. It is to be inferred thai 

 the range of >ii<iric<iiis here finds its northwestern limit. The San 

 Jacinto nigricans are all from the Pacific slope, as are also the 

 San Diego County series. Since specimens were taken at 

 Schain's. where were also secured examples referred to cabe- 

 :<>>uit. it appears that the ranges of the two forms may overlap 

 at least at this point. This was the only place where we found 

 any evidence of the overlapping of the ranges of any two species 

 of gophers, though this state of affairs is to be expected along 

 the lines where distinct species meet. The only alternative is 

 blending of forms through hybridization. This could be proved 

 by the collection of gophers in a practically continuous line from 

 one habitat into another up different sides of the mountain. 



