Fig. 168.—Chelmo marginalis, from the coast of Australia.
Only four species are known, locally distributed in the tropical seas. Ch. rostratus, the oldest species known, is said to have the instinct of throwing a drop of water from its bill so as to light upon any insect resting on a leaf, and thus make it fall, that it may instantly dart upon it. This statement is erroneous, and probably rests upon the mistaken notion that the long bill is especially adapted for this manœuvre, which, indeed, is practised by another fish of this family (Toxotes). The long slender bill of Chelmo (which is a true saltwater fish) rather enables it to draw from holes and crevices animals which otherwise could not be reached by it.
Heniochus.—One dorsal, with from eleven to thirteen spines, the fourth of which is more or less elongate and filiform. Snout rather short or of moderate length. Præoperculum without spine. Scales of moderate size.
Four species are known from the tropical Indo-Pacific. H. macrolepidotus is one of the most common fishes of that area; the species figured (H. varius) retains in a conspicuous manner horn-like protuberances on bones of the head, with which the young of all the species of this genus seem to be armed.
Fig. 169.—Heniochus varius.
Holacanthus.—Præoperculum with a strong spine at the angle. One dorsal, with from twelve to fifteen spines. Scales of moderate or small size.
Forty species are known, which, in their geographical distribution accompany, and are quite analogous to, the Chætodonts. One of the most common and most beautiful is called “Emperor of Japan” by the Dutch, which name has been adopted by Bloch for its specific designation, Holacanthus imperator. Its body is blue, longitudinally traversed by about thirty yellow bands; the ocular band, and the side behind the head, are black, edged with yellow; the caudal fin is yellow. It is a large species of this genus, sometimes attaining a length of 15 inches, and as an article of food is one of the most esteemed of all the Indian species. With regard to beauty of colours it is surpassed by another allied species, H. diacanthus, which likewise ranges from the east coast of Africa to Polynesia.
Pomacanthus differs from Holacanthus in having from eight to ten spines only in the dorsal fin.
The single species (P. paru) on which this genus is founded is one of the most common fishes of the West Indies, and offers one of the most remarkable instances of variation of colour within the limits of the same species: some specimens being ornamented with more or less distinct yellowish cross-bands, others with yellow crescent-shaped spots; in others black spots predominate.