1922] Kellogg: Synopsis of Microtus Mordax 299 



in the San Diegan faunal district uninterruptedly from the tidal 

 marshes of the seacoast to the boreal zone of adjacent mountains, upon 

 that of hemard/imus. This meadow mouse extends as high up in the 

 San Bernardino Mountains as Bluff Lake, 7500 feet altitude, where 

 it lives within the domain of 31. m. hernardinus. It has been pointed 

 out by Grinnell and Swarth (1913, pp. 348-349) that Microtus cali- 

 fornicus (neglectus) occupies, to the exclusion of any other Microtus 

 whatsoever, the ecological niche of Microtus mordax in the more 

 southern San Jacinto Mountains. Possibly mordax once lived in the 

 San Jacinto Mountains, as it does now in the San Bernardino Moun- 

 tains, but it has been replaced in the former by calif ornicns through a 

 process of upward invasion by that species from its adjacent lowland 

 habitat of a much larger extent. 



