First report of the megathyridid (Terebratellidina) brachiopod Argyrotheca from a hydrocarbon seep deposit, middle Eocene Humptulips Formation, Washington State, USA

A single terebratulide brachiopod valve found in a middle Eocene limestone deposit in the Humptulips Formation in western Washington State is the first record of a megathyridid brachiopod in a hydrocarbon seep deposit, the first fossil record of the genus Argyrotheca in western North America, and the northernmost record for Argyrotheca from the north-eastern Pacific Ocean.