Several specimens of a new trace fossil, Polycylindrichnus prolifer, n. gen., n. sp., have been collected from the Middle Silurian Thorold Formation in Hamilton, Ontario. Traces are multiple burrows, originating from a common source at depth, budding into several cylindrical to conical, subhorizontal burrows. Burrow openings lie on a common bedding plane. Traces are tentatively attributed to the activities of infaunal tunicates.