This well known genus of Old Red Sandstone Fishes was first named and described by Agassiz in his great work, the “Poissons Fossiles,” vol. ii. page 128. It is there classed with the Acanthodean family, which it somewhat resembles in the character and structure of its small rhomboidal scales; and also (according to Agassiz), in possessing Branchiostegal rays. This characteristic, however, as will afterwards be shown, appears to me to be founded on a misapprehension of the true nature of a series of elongated plates, situated below the lower jaw, which seem peculiar to this genus. The many points in which it very widely differs from the Acanthodeans induced the late Hugh Miller to suggest its removal altogether from them; and a distinct family, which he names Cheirolepini, is formed for its reception by Pander.