A group of trace fossils that is given a name because the similarity of the traces suggests they were made by closely related species of organisms. Ichnological taxonomy, which applies the principles of biological nomenclature to non-biological material, is governed by the International Code of Zoological Nomenclature. Above the level of genus, the Code indicates names should be used formally only to the family level; at higher levels all names are informal. Names of ichnogenera are conventionally written italicized and with a capital initial; ichnogenus is abbreviated as igen. See diplocraterion; rhizocorallium; zoophycus.