The Dayton, Osgood, and Laurel Formations and the Euphemia, Springfield, and basal part of the Cedarville Dolomites near the axis of the Cincinnati Arch in northeast Preble County, Ohio, belong in the uppermost part of the Ozarkodina sagitta rhenana to lower part of the Ozarkodina? crassa Chronozone and are late early to middle Wenlockian in age. The Dayton–Cedarville succession on the eastern flank of the Cincinnati Arch in north-central Greene County, Ohio, belongs in the uppermost part of the Pterospathodus celloni to upper part of the Ancoradella ploeckensis Chronozone and is late Llandoverian to early middle Ludlovian in age.The sea transgressed across the exposed and eroded Brassfield Formation to begin deposition of the Dayton Formation on the eastern flank of the Cincinnati Arch in Greene County, Ohio, during the late Llandoverian and completely flooded all of west-central Ohio by the late early Wenlockian. The region remained covered by a sea of fluctuating depth during deposition of the Dayton Formation–Cedarville Dolomite succession from the Wenlockian through early middle Ludlovian.Kockelella walliseri (Helfrich) evolved from K. ranuliformis (Walliser) during the middle Wenlockian (upper part of Ozarkodina sagitta rhenana Chronozone) by development of a lateral process adjacent to the cusp on the Pa element and by minor modification of the Pb element and some of the ramiform elements. Specimens from upper Llandoverian and lower Wenlockian strata previously assigned to K. walliseri belong to a different species, Kockelella sp. A Fordham, 1991. The evolutionary trends in the K. walliseri lineage, progressive restriction of the basal cavity and increasing development of the length of the lateral processes in the Pa element, parallel the trends in the K. amsdeni–K. stauros–K. variabilis lineage and resulted in the divergence of Kockelella cf. K. stauros Bischoff, 1986, from the main lineage in the middle Wenlockian.