The genus Amphioxus was instituted by Mr Yarrell for the reception of a singular little animal which he received from Mr Couch. The characters of this genus, as given in the History of British Fishes, are, “Body compressed, the surface without scales, both ends pointed; a single dorsal fin extending the whole length of the back; no pectoral, ventral, anal, or caudal fins; mouth on the under part of the head, narrow, elongated, each lateral margin furnished with a row of slender filaments.”