A primitive variety of Palaeoaplysina laminaeformis Krotov is the primary biotic constituent of a two-meter-thick biostrome in the upper Ely Limestone of western Utah. Associated fusulinaceans and stromatoporoids indicate an early Desmoinesian (Middle Pennsylvanian) age, making it the oldest documented occurrence of non-ancestral Palaeoaplysina in the world. Plate-supported packstone with 40-60% interstitial peloidal mud and silt-size fossil debris constitutes the dominant biostrome rock fabric. During the Late Carboniferous, non-ancestral palaeoaplysinids were restricted to the Ely and Sublett basins of Utah and Idaho, respectively. By Early Permian time, however, they played a significant role in the construction of reefs and biostromes across the entire northern margin of Laurussia.