Conulariida, gen. indet.

One of the more puzzling Palaeozoic fossils: a slender four-sided pyramid, finely ribbed, built not of calcium carbonate like most shells but of calcium phosphate, in rows of narrow rods.

Conulariids are now generally regarded as scyphozoan cnidarians — relatives of the jellyfish — attached to the sea floor at the pointed end and feeding with tentacles from the open top. The four-fold symmetry is the strongest argument for that placement.

They are never common, and complete specimens are rare because the thin phosphatic wall crushes and flakes readily.