Cyathaspis

Cyathaspis is the type genus of the heterostracan order Cyathaspidiformes. Fossils are found in late Silurian strata in the Cunningham Creek Formation, New Brunswick, Canada and Europe, especially in the Downton Castle Sandstone of Great Britain and Gotland, Sweden. The living animal would have looked superficially like a tadpole, albeit covered in bony plates composed of the tissue aspidine, which is unique to heterostracan armor.
"Cyathaspis ludensis" is the earliest British vertebrate fossil. It was found in rocks at Leintwardine in Herefordshire, a noted fossil locality.