Hyolithes has been thought to be a brachiopod-sub or adjacent species. The Spence Shale is famous for its Cambrian fossils, Hyolithes was a conically shelled creature with a flat "lid" shell to close the opening in the conical shell. Hyolithes were also represented in the Burgess Shale.  Possibly the least symmetrical two-shelled animal ever to be. Cambrian, Spence Shale, Langston Formation, Olvid, Idaho, USA. 3" x 1" x 1", 1.7 oz.