The monogenean genus Dactylogyrus parasitizing gills of the North American cyprinid fish genus Nocomis was studied comprehensively. D. reciprocus Rogers, 1967, was recovered from Nocomis leptocephalus bellicus, and for the first time from N. 1. leptocephalus, N. 1. interocularis, N. micropogon, N. platyrhynchus, and N. raneyi. Two new species are described: D. effusus sp. n. was taken only from N. effusus, and D. lachneri sp. n. from N. asper, N. biguttatus, and N. effusus. These three morphologically similar monogeneans are placed in the Reciprocus species group. Fishes of the cyprinid genus Nocomis are distributed over the eastern and most of the central United States and parts of southern Canada. They are divided into three species groups, namely, Biguttatus species group-N. biguttatus, N. asper, N. effusus; Micropogon species group-N. micropogon, N. platyrhynchus, N. raneyi; and Leptocephalus species group-N. leptocephalus leptocephalus, N. 1. interocularis, N. 1. bellicus (Lachner and Jenkins, 1967, and unpublished; Lachner and Wiley, unpublished). Rogers and Mizelle (1966) described the monogeneans Dactylogyrus absidatus and D. bellicae from the gills of N. 1. bellicus and later Rogers (1967) described D. limulus and D. reciprocus from the same host. The present report describes D. effusus sp. n. and D. lachneri sp. n. and groups them with D. reciprocus as the Reciprocus species group. MATERIALS AND METHODS Samples of the fish gills were collected from the United States National Museum (USNM) Fish Collection, the Tulane University Ichthyology Collection, the Auburn University Ichthyology Collection, the University of Michigan, Museum of Zoology, and personal collections. Most of the fish specimens were identified by Dr. E. A. Lachner of the Smithsonian Institution, Washington, D. C., who is currently reporting on their systematics, evolution, and behavior. Gill materials from museum collections were transferred to 40% ethyl alcohol for preservation. Preserved parasites were mounted in glycerine jelly. Live parasites were mounted using the method described by Malmberg Received for publication 8 June 1971. * Supported by the Southeastern Cooperative Fish Disease Project and partially by Rockefeller Foundation RF 65061 and Alabama Cooperative Fishery Unit, Auburn University. (1957). Mounts were ringed with a commercial slide sealer, Zut, produced by Bennett's Paint Products, Salt Lake City, Utah. To avoid contamination from the sediment of preserved specimens, parasites were taken directly from the host's gills just before mounting. Semichon's carmine and fast green stains were applied to aid the study of anatomy. Each sclerotized element of the parasite was isolated from adjacent tissues for drawing with the aid of a camera lucida. Measurements are in microns. Each average is followed by the range within parentheses. A total of 2,183 host fishes were examined and 2,484 dactylogyrids were mounted for systematic analyses. In this paper is abbreviated as R., drainage as dr., system as sys., and British Museum (Natural History) as BM(NH). The numerals in the parentheses following the drainages denote the fish collections made. DESCRIPTIONS OF DACTYLOGYRUS Reciprocus species group Diagnosis Four cephalic lobes, well separated on each side of cephalic area, all projecting anterolaterally. Four eyespots, similar in size; members of both pairs about same distance apart; eyespot granules may be dissociated to some extent. Pharynx small, circular in dorsal view. Peduncle moderately thick but distinct. Copulatory complex large, with thinwalled curved cirrus. Accessory piece bifurcate; main fork much longer than lateral process. Haptor large, hexagonal or bell-shaped with jagged edge. Ventral haptoral bar conspicuous, more slender but longer than dorsal haptoral bar. Anchors large; base with superficial root less than twice as long as deep root; shaft slightly curved and more than twice as long as point. Hooks large; with proportionately large base and short shaft; those close to median region larger than those on margin of haptor. Dactylogyrus effusus sp. n. (Figs. 1-8) Type host and locality: Nocomis effusus, USNM 205382, Green River drainage, Long Fork, tributary of Salt Lick Creek, 2.25 air miles northeast of Galen, Macon County, Tennessee.