Xiphias
in ichthyology, a genus of Xiphiidæ, distinguished by the absence of ventral fins. The best known species is X. gladius, the common or Mediterranean swordfish. Günther says that the distinction of species is beset with great difficulties because the form of the dorsal, the length of the ventrals, and the shape and length of the sword change according to the age.
X-RAY. See ROENTGEN RAYS.