G. L. Hoffman R.E. Putz 1963 <p><span><i>Gyrodactylus atratuli</i> from the blacknose dace (<i>Rhinichthys atratulus</i>) and the pearl dace (<i>Semotilus margarita</i>) is compared with known species of <i>Gyrodactylus</i> from North American fishes and described as a new species. <i>Gyrodactylus margaritae</i> from the pearl dace (<i>Semotilus margarita</i>) is compared with known species of <i>Gyrodactylus</i> from North American fishes and described as a new species. The average number of <i>G. atratuli</i> per blacknose dace in the natural habitat is 7.8 (1 to 32) and in the laboratory at the same water temperature after 55 days in captivity, 5.4 (0 to 11). <i>G. atratuli</i> and <i>G. margaritae</i> fail to live and reproduce on fish kept in nonrunning water at between 19 and 26 C in laboratory aquaria, but will live and reproduce in running spring water at 12 C in laboratory aquaria. An illustrated synopsis with a comparative table of measurements of known North American <i>Gyrodactylus</i> and a list of the species with brief reference to their differentiating characteristics are given.</span></p> application/pdf 10.2307/3275760 en American Society of Parasitologists Two new Gyrodactylus (Trematoda: Monogenea) from cyprinid fishes with synopsis of those found on North American fishes article