Phosphatic fossil fragments, commonly having less than 2 mm. maximum size, occur in acid residues of Ordovician rocks. A variety of fossil shapes has been found in te El Paso Group of west Texas, Simpson Group of Oklahoma, Dutchtown Formation of Missouri, and Maquoketa Group of Indiana. Excluding atermate brachiopods and conodonts, the collection reported here has greatest affinity to early ostracoderm fish and arthropods. Focus on these phosphatic microfossils can enhance our knowledge of the early evolution of phosphate-bearing organisms and their biostratigraphic significance Includes bibliographical references (p. 8-9) Phosphatic fossil fragments, commonly having less than 2 mm. maximum size, occur in acid residues of Ordovician rocks. A variety of fossil shapes has been found in te El Paso Group of west Texas, Simpson Group of Oklahoma, Dutchtown Formation of Missouri, and Maquoketa Group of Indiana. Excluding atermate brachiopods and conodonts, the collection reported here has greatest affinity to early ostracoderm fish and arthropods. Focus on these phosphatic microfossils can enhance our knowledge of the early evolution of phosphate-bearing organisms and their biostratigraphic significance Fieldiana series has been published as Geological Series by Field Columbian Museum (1895-1909) and Field Museum of Natural History (1909-1943), and as Fieldiana: Geology by Chicago Natural History Museum (1945-1966) and Field Museum of Natural History (1966-)