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Freshwater unionid bivalves are spatially and temporally distributed throughout the Morrison depositional basin, and locally dominate the biomass of many aquatic depositional environments. Two bivalve assemblages are identified. Within-channel assemblages are death assemblages that have been transported and may represent mixed assemblages from multiple communities. These assemblages are predominately disarticulated, in current stable orientations, and composed of higher stream velocity ecophenotypes (medium size, lanceolate form, and very thick shells). The floodplain-pond assemblages are disturbed neighborhood assemblages in the mudstones inhabited during life. The bivalves are predominately articulated, variable...
Field collections at more than 2900 sites and the examination of many museum collections and literature allowed me to map the historical and current distribution of several freshwater molluscan faunal groups in the Intermountain region of the United States (Great Basin, Colorado River drainage basin, and upper Snake River sub-basin). Historical and current records show that Margaritifera falcata, Anodonta californiensis, and Ferrissia rivularis have drainage-specific distributions, while Valvata utahensis has a specific drainage pattern, and V. californica (new combination) has a dispersed pattern. Shell morphometric data of Valvata and Ferrissia show extensive shell variation between and within populations. Current...