thelodus

from The Century Dictionary.

• noun An extinct genus of fishes of the subclass Ostracodermi, of the family Cœglolepidæ, characterized by small, quadrangular, and nearly uniform dermal tubercles, by a small dorsal fin near the base of the heterocercal tail, and by the absence of enlarged ridge-scales: from the Ludlow bone-bed and Oesel limestone of the. Upper Silurian and the Lower Old Red Sandstone.