1922] Kellogg: Calif ornlan Forms of Microtus Montanus 271 



warrant the recognition of dutcheri as a full species, even though so 

 far as known there is no geographic continuity between these two 

 forms. The characters which are used to distinguish chitcheri from 

 yosenvite are of less importance than those that separate either mon- 

 taniis from mordax or montanus from oalifornicus. The mere fact 

 that certain stocks are isolated from near allied stocks does not in 

 itself afford adequate grounds for the recognition or evaluation of 

 these isolated stocks as full species. For this reason the writer has 

 deemed it necessary to place dutcheri as a subspecies in the Microtus 

 montanus group. A careful study of a large series of skins and skulls 

 has shown that it is a closely allied and no doubt a comparatively 

 recent offshoot within this group. 



Marked physical barriers do not act with an equal degree of effect- 

 iveness on all the races of the different species of Microtus within the 

 state of California. In the Kings River region of the Sierra Nevada, 

 Microtus montanus is apparently absent; at any rate no specimens 

 have ever been collected there. On the north side specimens have 

 been taken only as far south as the meadows at the head of the San 

 Joaquin River ; these are referable to the race yosemite. In the Kings 

 River Caiion itself, Microtus mordax is the only meadow mouse. 

 Among animals, there is sometimes active antagonism between mem- 

 bers of the same genus. Microtus mordax is a wide ranging, active, 

 and aggressive species, not closely confined to any particular set of 

 surroundings. Its presence here in the limited areas suitable to 

 Microtus may afford an additional reason for the absence of Microtus 

 montanus from this caiion. 



From the foothills up as far as Lewis Creek, the floor of the caiion 

 is very narrow, but widens to a width of about half a mile from 

 Lewis Creek to its head near Bubb's Creek and Glacier Monument. 

 The valley itself is Transition; the surrounding tablelands some 

 twenty-five hundred feet above are Canadian. At the head of the 

 Kings River Valley the Canadian is hardly noticeable, as the Hud- 

 sonian and timber line are very quickly reached. The sides of the 

 Kings River Caiion are precipitous. The sheer rock cliffs on either 

 side are interrupted by a few narrow creeks emptying into the Kings 

 River below, and it is along these streams that Microtus mordax main- 

 tains its continuity of dispersal. In the valley, specimens of Microtus 

 mordax were trapped in a marshy meadow about a quarter of a mile 

 below Camp Kanawyer. Microtus calif ornicus nhariposae, a foothill 

 form, is not inhibited in its dispersal by the same factors which operate 



