What is "serrodiscus"

Serrodiscus is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It has been collected from the Lower Cambrian of Canada (Nova Scotia), Germany (Silesia), Poland (Holy Cross Mountains), Russia (Kuznetsk Alatau), the United Kingdom (Wales) and the United States (Massachusetts, New York State). It is named for the spines on the ventral side of the tailshield (or pygidium, which give it a serrated impression.