with a rhomboidal ornamentation that resembles that seen in Mongolitubulus, so some Mongolitubulus material may represent trilobites. Preservation The spines often comprise layers of phosphate, with a central void often infilled with diagenetic phosphate. Similar spines have been recovered from acid macerations, where they are preserved as films of organic carbon. Distribution Mongolitubulus is known from the Botomian to the lower strata of the Middle Cambrian, and have a worldwide distribution, being found on every continent including Antarctica. Rhombocorniculum is known from a variety of localities, including England and Massachusetts. References Cambrian arthropods Arthropod enigmatic taxa Prehistoric crustacean genera Controversial taxa Paleozoic life of Nova Scotia Paleozoic life of Quebec