This family has been formed for two extinct genera: Palæorhynchus from the schists of Glaris, and Hemirhynchus from tertiary formations near Paris. These genera resemble much the Trichiuridæ in their long, compressed body, and long vertical fins, but their jaws, which are produced into a long beak, are toothless, or provided with very small teeth. The dorsal fin extends the whole length of the back, and the anal reaches from the vent nearly to the caudal, which is forked. The ventrals are composed of several rays and thoracic. The vertebræ long, slender, and numerous, and, like all the bones of the skeleton, thin, indicating that these fishes were inhabitants of considerable depths of the ocean. Both the jaws of Palæorhynchus are prolonged into a beak, whilst in Hemirhynchus the upper exceeds the lower in length.
Eighth Division—Acanthopterygii Cotto-scombriformes.
Spines developed, in one of the fins at least. Dorsal fins either continuous or close together; the spinous dorsal, if present, always short; sometimes modified into tentacles, or into a suctorial disk; soft dorsal always long, if the spinous is absent; anal similarly developed as the soft dorsal, and both generally much longer than the spinous, sometimes terminating in finlets. Ventrals, thoracic or jugular, if present, never modified into an adhesive apparatus. No prominent anal papilla.
Marine fishes, with few exceptions.
First Family—Acronuridæ.
Body compressed, oblong or elevated, covered with minute scales. Tail generally armed with one or more bony plates or spines, which are developed with age, but absent in very young individuals. Eye lateral, of moderate size. Mouth small; a single series of more or less compressed, sometimes denticulated, sometimes pointed incisors in each jaw; palate toothless. One dorsal fin, the spinous portion being less developed than the soft; anal with two or three spines; ventral fins thoracic. Air-bladder forked posteriorly. Intestines with more or less numerous circumvolutions. Nine abdominal, and thirteen caudal vertebræ.
Inhabitants of the tropical seas, and most abundant on coral-reefs. They feed either on vegetable substances or on the superficial animal matter of corals.
Extinct species of Acanthurus and Naseus have been discovered in the Monte Bolca formation.
Acanthurus.—Jaws with a single series of lobate incisors, which are sometimes movable. An erectile spine hidden in a groove on each side of the tail. Ventral fins with one spine and generally five rays. Scales ctenoid, sometimes with minute spines. Branchiostegals five.
The fishes of this genus, which sometimes are termed “Surgeons,” are readily recognised by the sharp lancet-shaped spine with which each side of the tail is armed. When at rest the spine is hidden in a sheath; but it can be erected and used by the fish as a very dangerous weapon, by striking with the tail towards the right and left. “Surgeons” occur in all tropical seas, with the exception of the eastern part of the Pacific, where they disappear with the corals. They do not attain to any size, the largest species scarcely exceeding a length of eighteen inches. Many are agreeably or showily coloured, the ornamental colours being distributed in very extraordinary patterns. The larger species are eatable, and some even esteemed as food. It is stated that the fry of some species periodically approaches, in immense numbers, the coasts of some of the South Sea Islands (Caroline Archipelago), and serves as an important article of food to the natives. Nearly fifty species are known.