Fig. 209.—Cutlass-fish, Trichiurus lepturus Linnæus. St. Augustine, Fla.
The Palæorhynchidæ.—The extinct family of Palæorhynchidæ is found from the Eocene to the Oligocene. It contains very long and slender fishes, with long jaws and small teeth, the dorsal fin long and continuous. The species resembles the Escolar on the one hand and the sailfishes on the other, and they may prove to be ancestral to the Istiophoridæ. Hemirhynchus deshayesi with the upper jaw twice as long as the lower, sword-like, occurs in the Eocene at Paris; Palæorhynchum glarisianum, with the jaws both elongate, the lower longest, is in the Oligocene of Glarus. Several other species of both genera are recorded.
Fig. 210.—Palæorhynchus glarisianus Blainville. Oligocene. (After Woodward.)
The Sailfishes: Istiophoridæ.—Remotely allied to the cutlass-fishes and still nearer to the Palæorhynchidæ is the family of sailfishes, Istiophoridæ, having the upper jaw prolonged into a sword made of consolidated bones. The teeth are very feeble and the ventral fins reduced to two or three rays. The species are few in number, of large size, and very brilliant metallic coloration, inhabiting the warm seas, moving northward in summer. They are excellent as food, similar to the swordfish in this as in many other respects. The species are not well known, being too large for museum purposes, and no one having critically studied them in the field. Istiophorus has the dorsal fin very high, like a great sail, and undivided; Istiophorus nigricans is rather common about the Florida Keys, where it reaches a length of six feet. Its great sail, blue with black spots, is a very striking object. Closely related to this is Istiophorus orientalis of Japan and other less known species of the East Indies.
Tetrapturus, the spearfish, has the dorsal fin low and divided into two parts. Its species are taken in most warm seas, Tetrapturus imperator throughout the Atlantic, Tetrapturus amplus in Cuba, Tetrapturus mitsukurii and Tetrapturus mazara in Japan. These much resemble swordfish in form and habits, and they have been known to strike boats in the same way.
Fossil Istiophoridæ are known only from fragments of the snout, in Europe and America, referred provisionally to Istiophorus. The genus Xiphiorhynchus, fossil swordfishes from the Eocene, known from the skull only, may be referred to this family, as minute teeth are present in the jaws. Xiphiorhynchus priscus is found in the London Eocene.
The Swordfishes: Xiphiidæ.—The family of swordfishes, Xiphiidæ, consists of a single species, Xiphias gladius, of worldwide distribution in the warm seas. The snout in the swordfish is still longer, more perfectly consolidated, and a still more effective weapon of attack. The teeth are wholly wanting, and there are no ventral fins, while the second of the two fins on the back is reduced to a slight finlet.
