Palme 1935 Microtus californicus Angel Island, San Francisco Bay, Marin Co., Calif. Oct. 17 In a hike across the island, I saw many burrows and runways in the grass. Almost every grassy hill- side is riddled with holes and run- ways. Saw several mice in the runs. Oct. 19 Caught 12 in 23 gov. size mouse traps set along the edge of a road Traps every 15 paces in dry grass and weeds under Live Oaks and a few Elder bushes. About ½ the traps were set in Microtus runways. Nine of this species were caught both in runways and in such places as leafy slopes under live oaks or on bare open ground. 1 Trap caught 2 Microtus, a rather unusual thing. Both of these were almost completely eaten, probably by other Microtus. The great abundance of Microtus possibly may be accounted for by absence of competition from other species, since I caught no other kind of mice. Also it is quite possible that there are no carnivores on the island to keep the mice in check. I understand that