I. Cade 1958 Microlus oceconicus 19 August - Summary of occurrence in the Okfilek area I am more and more convinced that this species is mainly a dweller in lush reed- groves - willow complexes along the edge of small streams, slope drainages and around the margin of lakes. All the trapped date at this station support their point of view. In addition, I found heavy microlusine activity (sign) along the fresh drains which come down the swell of the valley between the alluvial fans. T2 cuts across such drains, but a transect paralleling one of the drains should have little sign. At this reason fresh diggings are the most conspicuous sign (also trace of M. microwes). These diggings are in the sides of drainage ditches, banks, at the foot of benches or in peat mounds, and they are quite conspicuous because the newly excavated peat and dirt is spread out as a kind of apronment in front of the hole. Such material is often reworked right into the burrow system. In one such area I set 8 traps in a space of 50 square feet. In two days, 6 Mo were taken in these traps. Along this drain a tran- sect probably would have yielded between 20 & 30 Mo, mostly juveniles & debile adults.