=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. [Illustration: FIG. 211.—Young Swordfish, _Xiphias gladius_ (Linnæus). (After Lütken.) ] The swordfish follows the schools of mackerel to the New England coasts. "Where you see swordfish, you may know that mackerel are about," Goode quotes from an old fisherman. The swordfish swims near the surface, allowing its dorsal fin to appear, as also the upper lobe of the caudal. It often leaps out of the water, and none of all the fishes of the sea can swim more swiftly. [Illustration: FIG. 212.—Swordfish, _Xiphias gladius_ (Linnæus). (After Day.) ]