The ostracod fauna and vertical changes in its composition were examined in a shale sequence of the 5-Yard Limestone cyclothem (Yoredale Series) at a locality in Bishopdale, N. Yorkshire. The ostracod tax a are mainly confined to three superfamilies: Kirkbyacea, Healdiacea and Bairdiacea. The co-occurrence of several relatively short-ranging species such as <i>Kirkbya quadrata, Cribroconcha insculpta</i> and <i>Bairdiolites elevatus</i> suggests a Late Brigantian age. Four new species are described: <i>Cornigella posteroextensa, ? Eriella minima, Rectobairdia bavarica</i> and <i>Roundyella binoda.</i><br/><br/>Fluctuations in influx of terrigenous mud and water turbulence, related to delta growth, appear to have been the main environmental parameters that controlled the ostracod distribution and abundance along a nearshore-offshore gradient. Three different ostracod assemblages are recognized. A <i>Roundyella-Cribroconcha</i> assemblage, dominated by kirkbyacean and healdiacean ostracods, represents a quiet, nearshore environment with a fairly high depositional rate of terrigenous mud. A <i>Bairdia</i> assemblage, higher in the section, is dominated by bairdiacean ostracods that lived in a more turbulent, relatively offshore environment with less input of terrigenous sediment. A third, intermediate assemblage consists of almost equal amounts of bairdiacean and kirkbyacean ostracods, and reflects a transition from the <i>Bairdia</i> to the <i>Roundyella-Cribroconcha</i> assemblage.