Lichadian trilobites

The classification of the group of trilobites formerly placed under the family Lichadidae is here revised in the light of the morphology and the evolution. The group is designated a super-family, the Lichadacea, and divided into two families, the Lichadidae and the Trochuridae. The Lichadidae include the subfamilies Lichadinae, Tetralichadinae, Homolichadinae, and Gaspelichadinae; the Trochuridae, the subfamilies Trochurinae, Hemiarginae, Dicranopeltinae, and Platylichadinae. The genera are redescribed; 17 new genera are proposed. It is pointed out that the lichad glabella is composed of six segments, and is derived from a form with four pairs of lateral glabellar furrows. Studies of the geographic distribution indicate that the greatest evolution occurred in northern Europe and that there were two migrations to North America, one by way of northern Greenland.