Urodermal bones are found in the species of the subfamily Lampanyctinae of the Myctophidae, although some species of Diaphus, Lampanyctus and Taaningichthys lack them. One urodermal occurs in the tendon of the epaxial caudal muscle which inserts on the ninth caudal-fin ray. The occurrence of urodermals in the tendon raises the question of their homology. They may be homologous with the rhombic scales of the Jurassic teleosts in which case they have lost their enamel layer, or they may be newly formed structures in the tendon of the epaxial caudal muscle. Further search for the distribution of urodermals will be needed to clarify the homology.