The remarkable changes which Sword-fishes undergo at an early stage of their growth have been noticed above, p. 173 and seq.
Sword-fishes are as old a type as the Berycoids. Their remains have been found in the chalk of Lewes, and more frequently in the London clay of Sheppy, where an extinct genus, Coelorhynchus, has been recognised.
Seventh Division—Acanthopterygii Trichiuriformes.
Body elongate, compressed or band-like; cleft of the mouth wide, with several strong teeth in the jaws or on the palate. The spinous and soft portions of the dorsal fin and the anal are of nearly equal extent, long, many-rayed, sometimes terminating in finlets; caudal fin forked, if present.
Family—Trichiuridæ.
Marine fishes inhabiting the tropical and sub-tropical seas; some of them are surface-fishes, living in the vicinity of the coast, whilst others descend to moderate depths, as the Berycoids. All are powerful rapacious fishes, as is indicated by their dentition.
The oldest of the extinct genera are Enchodus and Anenchelum; they were formerly referred to the Scombroids, but belong to this family. The former has been found in the chalk of Lewes and Mæstricht; the latter is abundant in the Eocene schists of Glaris. Anenchelum is much elongate, and exhibits in the slender structure of its bones the characteristics of a deep-sea fish; it resembles much Lepidopus, but has some long rays in the ventrals. Other Eocene genera are Nemopteryx and Xiphopterus. In the Miocene of Licata in Sicily Trichiuridæ are well represented, viz. by a species of Lepidopus, and by two genera, Hemithyrsites and Trichiurichthys, which are allied to Thyrsites and Trichiurus, but covered with scales.
The following is a complete list of the genera referred to this family:—
Nealotus.—Body incompletely clothed with delicate scales. Small teeth in the jaws and on the palatine bones; none on the vomer. Two dorsal fins, the first continuous and extending to the second; finlets behind the second and anal fins. Each ventral fin represented by a single small spine. A dagger-shaped spine behind the vent. Caudal fin well developed.
One specimen only of this fish (N. tripes), 10 inches long, has been obtained off Madeira; it evidently lives at a considerable depth, and comes to the surface only by accident.