They were discovered in the first half of the 19th century in the Old Red Sandstone of Britain. Louis Agassiz named it in 1835. He had been to Scotland, and seen Hugh Miller's collection. Miller described his collecting later, in a popular work on the rocks and fossils of the Old Red Sandstone in Scotland. Agassoz' single species has now been split into more species, some of which have been moved into a different genus.