During the past summer, while on a visit to the northern portion of this State, my attention was attracted to the presence of numerous mudcells on the lower surface of stones lying along the bands of the Wapsipinicon River, These cells, most of them empty, with one end forced off, somewhat resembled the single one with which some or our common mud-wasps start their establishment of the ceilings of little-used rooms, or on the rafters of outhouses, but very much smaller. The largest measure about 12 mm, in length and 8 mm, in breadth, while the small ones are only 5 mm. long and 2.5 mm wide.