During the past summer (1909) while at Havana, Ill., in con nection with the reopening of the Biological Station of the Illinois State Laboratory of Natural History, the writer was surprised to find at one location numerous colonies of a hydroid which pre sumably belongs to the genus Cordylophora. A superficial examination of the animal and of the literature involved has not disclosed any' reason why it may not prove to be C. lacustris Ailman which is a species of hydroid commonly found in brackish water and less frequently in fresh water. Numerous colonies were found July 30 in a partially sub merged willow thicket near the north end of Quiver Lake which is really a part of the Illinois River near Havana. The majority of the colonies were attached to the submerged portions of living willow shoots while a few were found on the leaves and stems of other plants. A later visit was made to the same locality October i6 when the water of the lake was somewhat lower and no longer covered the spot at which the July collections were made. In the part of the thicket which was still submerged, numerous colonies were found attached to dead sticks and branches that projected from the bottom toward the surface. At each visit the collections were made in water less than two feet deep and over which a considerable layer of Lemna had accumu lated under the influence of west or northwest winds. In mid summer the colonies were in dense shade and were associated with a great variety of living organisms among which bryozoans were especially abundant.