The authors describe the adult of the trematode Floridatrema heardi n. gen, n. sp., parasite of the intestine of Oryzomys palustris (Mammalia:Rodentia) in Florida (USA). The new genus is placed among the Microphallidae, Maritrematidi, Maritrematinae, Maritrematini; near the genus Maritrema Nicoll, it is characterised by vitellaria in the form of a horseshoe and the anterior extension of two symmetrical uterine loops as far as the level of the pharynx, the left anterior uterine loop proceeding from the uterus proximally. The species lacks a spiny atrio-acetabular plate and concentric rings in the afferent sub-tegumentary musculature. The anotomical phenomenon of the anterior extension of the uterus in the Microphallidae is discussed.