Polyclithrum mugilini gen. et sp. n. is reported from Mugil cephalus L. from Lake Seminole, Georgia. This species was determined to be sufficiently different from all described gyrodactylids to warrant erection of a new subfamily, Polyclithrinae. It is distinguished by having the haptor supported by numerous sclerotized processes, by the anchor bases having deep and superficial roots, by having several accessory bars articulated to the anchors, and by the marginal hooks being distributed in two groups. The species described herein was collected as part of a survey of fish parasites being conducted by the Southeastern Cooperative Fish Parasite and Disease Project. Hosts were collected with the aid of an electric shocker. To determine whether the parasites inhabited the gills or the body of the hosts, the gills were removed and placed in one container and the body in another container of 1:4,000 formalin solution (Putz and Hoffman, 1963). After 1 hr, formalin was added to the containers to make a 5% solution. The parasites were later recovered for study in the laboratory from the solution containing the body. Specimens were treated and measured as described by Rogers and Wellborn (1965). All measurements are in microns. Averages of measurements are given followed by the range in parentheses. Drawings were made with a camera lucida. The keys to the members of Gyrodactylidae in Yamaguti (1963) were used to determine the status of the present species. Thanks are extended to Herbert Wyatt, Walter Godwin, and Mercer Norton of the Georgia Game and Fish Commission for assistance in collecting the host fish. Polyclithrinae subfam. n.