=The Pine-cone Fishes: Monocentridæ.=—Among the most extraordinary of all fishes is the little family of _Monocentridæ_, or pine-cone fishes. _Monocentris japonicus_, the best-known species, is common on the coasts of Japan. It reaches the length of five inches. The body is covered with a coat of mail, made of rough plates which look as though carelessly put together. The dorsal spines are very strong, and each ventral fin is replaced by a very strong rough spine. The animal fully justifies the remark of its discoverer, Houttuyn (1782), that it is "the most remarkable fish which exists." It is dull golden brown in color, and in movement as sluggish as a trunkfish. A similar species, called knightfish, _Monocentris gloriæ-maris_, is found in Australia. No fossils allied to _Monocentris_ are known. CHAPTER XVI PERCOMORPHI =SUBORDER Percomorphi, the Mackerels and Perches.=—We may place in a single suborder the various groups of fishes which cluster about the perches, and the mackerels. The group is not easily definable and may contain heterogeneous elements. We may, however, arrange in it, for our present purposes, those spiny-rayed fishes having the ventral fins thoracic, of one spine and five rays (the ventral fin occasionally wanting or defective, having a reduced number of rays), the lower pharyngeal bones separate, the suborbital chain without backward extension or bony stay, the post-temporal normally developed and separate from the cranium, the premaxillary and maxillary distinct, the cranium itself without orbitosphenoid bone, having a structure not greatly unlike that of perch or mackerel, and the back-bone primitively of twenty-four vertebræ, the number increased in arctic, pelagic, or fresh-water offshoots. The species, comprising the great body of the spiny-rayed forms, group themselves chiefly about two central families, the _Scombridæ_, or mackerels, and the _Serranidæ_, the sea-bass, with their fresh-water allies, the _Percidæ_, or perch. =The Mackerel Tribe: Scombroidea.=—The two groups of _Percomorphi_, the mackerel-like and the perch-like, admit of no exact definition, as the one fully grades into the other. The mackerel-like forms, or _Scombroidea_, as a whole are defined by their adaptation for swift movement. The profile is sharp anteriorly, the tail slender, with widely forked caudal; the scales are usually small, thin, and smooth, of such a character as not to produce friction in the water. In general the external surface is smooth, the skeleton light and strong, the muscles firm, and the species are carnivorous and predaceous. But among the multitude of forms are many variations, and some of these will seem to be exceptions to any definition of mackerel-like fishes which could possibly be framed.