OH, THOSE RUSSIANS: CHEIRURUS INGRICUS

This glorious rich chocolate showboat is the trilobite Cheirurus ingricus from Middle Ordovician limestone deposits in the Wolchow River Region of Saint Petersburg, Russia. 

We sometimes find these lovelies enrolled or semi-enrolled with their impossibly thin genal spines lifted in the air. The Cheirurids appeared about 500 million years ago and died out about 390 million years ago. They are definitely a favourite!