Wikipedia
Mesonacis
Mesonacis is an extinct genus of trilobite that lived during the Botomian, found in North-America (excluding Greenland), and the United Kingdom (North-Western Scotland). Some of the species now regarded part of Mesonacis, have previously been assigned to Angustolenellus or Olenellus (Angustolenellus). Angustolenellus is now regarded a junior synonym of Mesonacis.