What is "semadiscus"

Semadiscus is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It has been collected from the Lower Cambrian (early Botomian) of Canada ( Newfoundland), Russia ( Siberia, Gorno-Altaysk), and the United States ( New York State). Only the headshield (or cephalon) is known, and it may well be that it would be better to include it in Serrodiscus.