Nonmarine ostracode species are indicative of the physical and chemical nature of lacustrine environments. Although salinity has traditionally been regarded as one of the more important parameters that affect the occurrence patterns of lacustrine ostracodes, examination of the solute composition and salinities of the lakes where Limnocythere sappaensis and L. staplini live reveals that solute composition and not salinity is the most critical factor that controls their occurrence. The occurrence of these taxa in the modern world is mutually exclusive. L. sappaensis lives in water that is enriched in Na+-HCO3−- and depleted in Ca2+. L. staplini lives in water that is enriched in various combinations of Na+-Mg2+-Ca2+--Cl− and is depleted in HCO3. These solute compositions are the product of the mineral fractionation processes described by Eugster and Hardie. The positive correlation between these two species occurrences and the mineralogic fractionation processes suggests that these taxa may be used as reliable paleohydrochemical indicators. Studies in progress dealing with other ostracode taxa suggest that saline lacustrine ostracodes can provide a precise method for reconstructing paleohydrochemistry.