Frustule ultrastructure of Pleurosira laevis (Ehr.) Compère from an epilithon sample collected from the Missouri River was examined using scanning electron microscopy. Valve characteristics were similar to those found by other authors, whereas certain features of the cingulum were new. The cingulum consists primarily of three girdle bands (a valvocopula and two pleurae). The valvocopula can be complete but open at one end, below the ocellus. However, it is more commonly bisegmented, with two narrow and severable connecting points located in the pars interior region underlapping the mantle. The first and second pleurae are either biligulate or uniligulate and closed, but the former, when uniligulate, may be an open band as well. The second pleura is narrower and more delicate than the first. When a natural cleavage of a band subtends a ligula, the band is prone to break along the cleavage during specimen preparation, thus making difficult the assessment of band form and cingulum arrangement. Regions of band overlap have smooth poreless edges, whereas those of underlap are rimmed with either fine fimbriae or, occasionally, a coarser comblike fringe. The variability of the bands results in a cingulum that can be assembled in at least four different arrangements.