Elrathia kingii is a trilobite species commonly found in the Wheeler Formation of Utah, USA. It is medium-sized, with large specimens measuring approximately 4–5 cm in length, and lived 500 million years ago during the Cambrian Period. Like all trilobites, it was an extinct marine arthropod that inhabited the seabed in the early history of animal life.

It could inhabit oxygen-poor environments in which few other organisms could survive. Such conditions also favoured fossil preservation, helping explain the abundance of its fossils.

The pictured example consists of a sedimentary rock matrix containing a trilobite exoskeleton shed during growth and moulting. The exoskeleton subsequently mineralised and was preserved in the sedimentary rock.

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