The genus Monobothrium Diesing, 1863 includes two Palaearctic species (parasitizing cyprinids, possessing postovarian vitelline follicles, lacking an external seminal vesicle and having digitiform or cuneicrispitate scolex) and five Nearctic species (parasitizing catostomid fish, lacking postovarian vitelline follicles, possessing an external seminal vesicle and having loculomonobothriate, monobothriate or loculotruncate scolex). Based on these morphological differences, supported by preliminary molecular data, five North American species (originally placed in Monobothrium) are proposed to be transferred to Promonobothrium Mackiewicz, 1968 as new combinations. European species Monobothrium auriculatum Kulakovskaya, 1961 should be transferred to Caryophyllaeus Gmelin, 1790 as C. auriculatus n. comb. As a result of this transfer, Monobothrium becomes monotypic, with M. wageneri Nybelin, 1922 representing its only species.