Monoclea occurs in Jamaica in very damp places, being usually constantly wet with dripping water. The male receptacle of Monoclea is only superfically like that of Fegatella, since all the antheridia of a receptacle are formed in acropetal succession from one growing point. It resembles rather that of Corsinia and Fimbriaria. The antheridium rudiment is elongated, and it divides transversely into six or seven primary cells. The wall cells and spermatogenous cells are separated from each other in the body of the antheridium after the formation of quadrant and octant walls. The mature antheridium is elongated and pointed and is sunken in the receptacle. In the nucleus of the spermatozoid the individual chromosomes are recognizable as distinct twisted fibers. The archegonium is very long-necked, has six rows of neck cells and twelve or more neck canal cells. It is probably fertilized before the hood-like involucre has grown far beyond its tip. The capsular portion of the sporogonium divides to quadrants and octants before sporogenous cells and wall cells are separated. The foot is small, the seta stretches to 30 or 40mm in length, and the extended capsule is erect, elongated, cylindrical, and its wall is a single layer of cells. Monoclea possesses two kinds of rhizoids, corresponding to those of Marchantia in size, direction of growth, and in the presence of tubercles in those of one type. The absence of air chambers and ventral scales is probably due to the nearly aquatic habit of the plant. The evidence gained from the study of the origin and structure of the male receptacle, and of the antheridium and archegonium, and from the structure of the wall of the capsule, and the presence and direction of growth of the two types of rhizoids, favors the view that Monoclea is most closely related to the lower Marchantiaceae.