This may be a bit late, but the type of preservation and color look a lot like fossils from the Mahantango Formation that pops up throughout central Pennsylvania… If he was wondering what formation they may have come from.
@asa-kaplan @bmacfadden @jayson-kowinsky We have brachs that look like that here in Ohio. The ones you show as molds are dead ringers for the Silurian Pentamerus sp pictured in Fossils of Ohio. We do not have a Devonian one here that looks like that. The Treatise shows Pentamerus is only Silurian although the Pentameridae do range into the Devonian. So perhaps yours are in that group. – Jack