Echinoids are poorly known from the Devonian of SW England. This report records an external mould of a solitary primary spine in a chert cobble collected from near the site of Wolborough Quarry, SW Devon, a well-known Middle Devonian palaeontological site. However, cherts are rare in Devonian limestones of south Devon and the spine is unusually robust in comparison with those of other Devonian taxa. The cobble is here interpreted as an erratic, most probably an Upper Cretaceous flint, and the spine is identified as Prionocidaris sp. cf. P. vendocinensis (Agassiz & Desor). This is another illustration of the high fidelity possible in fossils preserved in cherts even after reworking.