Phosphatic microfossils including copious microvertebrates and conodont elements indicative of the upper Icriodella discreta-Icriodella deflecta Zone (Aeronian) are found in a single bed of the Hendricks Formation, Burnt Bluff Group, Sturgeon Bay, Wisconsin. Scales of thelodonts, including Loganellia sp. cf. Loganellia siberica Karajute-Talimaa, 1978, and rare Valyalepis crista Turner (in Turner and Nowlan, 1995) predominate among the microvertebrate remains. Most scales are referred to Zuegelepis potanus Turner new genus and species. Associated with the thelodont scales are rare phosphatic fragments of questionable dermal "bone" and scales, possibly of heterostracan origin. Thelodont scales are also found in the Hendricks Formation at Fayette State Park, Michigan and in the subsurface Byron Formation (Burnt Bluff Group) in Schoolcraft County, Michigan.