=The Butterfly-fishes: Chætodontidæ.=—The central family of _Squamipinnes_ is that of the butterfly-fishes or _Chætodontidæ_. In this group the teeth are distinctly brush-like, the mouth small, the dorsal fin continuous and closely scaly, and the ventral fins with one spine and five rays. The species are mostly of small size and brilliant and varied coloration, yellow and black being the leading colors. They vary considerably with age, the young having the posterior free edges of the bones of the head produced, forming a sort of collar. These forms have received the name of _Tholichthys_, but that supposed genus is merely the young of _Chætodon_. The species of _Chætodontidæ_ abound in rock pools and about coral reefs in clear water. They are among the most characteristic forms of these waters and their excessive quickness of movement compensates for their conspicuous coloration. In these confined localities they have, however, few enemies. The broad bodies and spinous fins make them rather difficult for a large fish to swallow. They feed on small crustaceans, worms, and the like. The analogy to the butterfly is a striking one, giving rise to the English name, butterfly-fish, the Spanish mariposa, and the Japanese chochouwo, all having the same meaning. Fossil chætodonts are rather few, _Chætodon pseudorhombus_ of the Pliocene of France, _Holocanthus microcephalus_ and _Pomacanthus subarcuatus_ of the Eocene, being the only species recorded by Zittel. [Illustration: FIG. 339.—Black Angel-fish, _Pomacanthus arcuatus_ (Linnæus). Barnegat, New Jersey. ] In the principal genus, _Chætodon_, the colors are especially bright. There is almost always a black bar across the eye, and often black ocelli adorn the fins. This genus is wanting in Europe. _Chætodon capistratus_, _striatus_, and numerous other species are found in the West Indies; _Chætodon humeralis_ and _nigrirostris_ are common on the coast of Mexico. The center of their distribution is in Polynesia and the East Indian Archipelago. _Chætodon reticulatus_, _lineolatus_, _ulietensis_, _ornatissimus_, _ephippion_, _setifer_, and _auriga_ are among the most showy species. Numerous closely related genera are described. In some of these the snout is prolonged into a long tube, bearing the jaws at its end. Of this type are _Chelmo_ in India, _Forcipiger_ in Polynesia, and _Prognathodes_ in the West Indies. _Heniochus_ (_macrolepidotus_) has one dorsal spine greatly elongated. _Microcanthus strigatus_, one of the most widely distributed species, is known by its small scales. _Megaprotodon_ (_triangularis_) has four anal spines instead of three as in the others. [Illustration: FIG. 340.—Angel-fish or Isabelita, _Holacanthus ciliaris_ (Linnæus). Jamaica. Family _Chætodontidæ_. ]