The Squamipinnes.—Very closely allied to the Percomorphi is the great group called Squamipinnes (squama, scale; pinna, fin) by Cuvier and Epelasmia by Cope. With a general agreement with the Percomorphi, it is distinguished by the more or less complete soldering of the post-temporal with the cranium. In the more specialized forms we find also a soldering of the elements of the upper jaw, and a progressive reduction in the size of the gill-opening. The ventral fin retains its thoracic insertion, and, as in the perch mackerel-like forms, it has one spine and five rays, never any more. The ventral fins are occasionally lost in the adult, as in the Stromateidæ, or they may lose part of their rays. The name Squamipinnes refers to the scaly fins, the typical species having the soft rays of dorsal, anal, and caudal, and sometimes of other fins densely covered with small scales. In various aberrant forms these scales are absent. The name Epelasmia (ἔπι, above; ἐλάσμος, plate) refers to the thin upper pharyngeals characteristic of certain forms. The transition from this group to the Sclerodermi is very clear and very gradual. The Squamipinnes, Sclerodermi, Ostracodermi, and Gymnodontes form a continuous degenerating series. On the other hand the less specialized Squamipinnes approach very closely to forms already considered. The Antigoniidæ are of uncertain affinities, possibly derived from such forms as Histiopteridæ, while Platax show considerable resemblance to scaly-finned fishes like the Kyphosidæ and Stromateidæ. The Scorpididæ seem intermediate between Stromateidæ and Platacidæ. In such offshoots from Scombroidei or Percoidei the group doubtless had its origin.

We may begin the series with some forms which are of doubtful affinity and more or less intermediate between the Squamipinnes and the more primitive Percomorphi.

The Scorpididæ.—This family has the general appearance of Platax and Ilarches, but the teeth are not brush-like, and the post-temporal is free from the skull as in perch-like fishes. The species inhabit the Pacific. Scorpis georgianus is a food-fish of Australia, with the body oblong. Monodactylus argenteus, the toto of Samoa, is almost orbicular in form, while Psettus sebæ is twice as deep as long, the deepest-bodied of all fishes in proportion to its length.

The Boarfishes: Antigoniidæ.—The boarfishes (Antigoniidæ) are characterized by a very deep body covered with rough scales, the post-temporal, as in the Chætodontidæ and the Zeidæ, being adnate to the skull.

These fishes bear some resemblance to Zeus, but there is no evidence of close affinity nor is it clear that they are related to the Chætodontidæ. Capros aper, the boarfish, is common in southern Europe, reaching a length of less than a foot, the protractile mouth suggesting that of a pig. The diamond-fishes, Antigonia, are deeper than long and strongly compressed, the body being covered with roughish scales. The color is salmon-red and the species live just below the depths ordinarily explored by fishermen. Antigonia capros is found at Madeira and in the West Indies, Antigonia steindachneri about Hawaii and in Japan, while the smaller Antigonia rubescens is abundant in the Japanese bays at a depth reached by the dredge. An extinct genus, Proantigonia from the Miocene is said to connect Antigonia with Capros.

The Arches: Toxotidæ.—The archers, Toxotidæ, have the body compressed, the snout produced, and the dorsal fin with but five spines. The skeleton differs widely from that of Chætodon and the family should perhaps rather find its place among the percoids. Toxotes jaculatrix is found in the East Indies. The name alludes to its supposed habit of catching insects by shooting drops of water at them through its long mouth.

The Ephippidæ.—With the typical Squamipinnes, the teeth become very slender, crowded in brush-like bands. The least specialized family is that of Ephippidæ, characterized by the presence of four anal spines and a recumbent spine before the dorsal. The principal genus, Ephippus (Scatophagus), is represented by Ephippus argus, a small, bass-like fish, spotted with black, found in the Indian seas, and ranging northward to Formosa. Species referred to Ephippus (Scatophagus) are recorded from the Italian Eocene of Monte Bolca, where a species of Toxotes has been also found.

The Spadefishes: Ilarchidæ.—In the Ilarchidæ the dorsal is divided into two fins, the spinous part being free from scales. In various regards the species are intermediate between ordinary perch-like forms and the chætodonts. In these fishes the body is very deep and, with the soft fins, closely covered with roughish scales. In Ilarches (Ephippus), represented by Ilarches orbis of the Indian seas, these scales are relatively large. This species is a common food-fish from India to Formosa.

In the American genus, Chætodipterus, the scales are quite small. The spadefish (Chætodipterus faber), sometimes called also moonfish or angel-fish, is a large, deep-bodied fish, reaching a length of two feet. It is rather common from Cape Cod to Cuba, and is an excellent pan fish, with finely flavored white flesh. The young are marked by black cross-bands which disappear with age, and in the adult the supraoccipital crest is greatly thickened and the skull otherwise modified. A very similar species, Chætodipterus zonatus, occurs on the west coast of Mexico. Species allied to Chætodipterus are fossil in the Italian Eocene. The Drepanidæ of the East Indies are close to the Ilarchidæ. Drepane punctata is a large, deep-bodied fish resembling the spadefish but with larger scales.

The Platacidæ.—Closely related to the Ilarchidæ is also the East Indian family of Platacidæ, remarkable for the very great depth and compression of the body, which is much deeper than long, and the highly elevated dorsal and anal still further emphasize this peculiarity of form. In this group the few dorsal spines are closely attached to the soft rays and the general color is dusky. In the young the body is deeper than in the adult and the ventral fins much more produced. The best-known species is the tsuzume or batfish (Platax orbicularis), which ranges from India through the warm current to northern Japan. Platax teira, farther south, is very similar. Platax altissimus, with a very high dorsal, is a fossil in the Eocene of Monte Bolca.

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.

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.

The species of Holacanthus, known as angel-fishes, are larger in size, and their colors are still more showy, being often scarlet or blue. In this genus the preopercle is armed with a strong spine, and there are fourteen or more strong spines in the dorsal. This genus has also its center of distribution in the East Indies, whence two species (septentrionalis and ronin) with concentric stripes of blue range northward to Japan. Holacanthus tibicen, jet-black with one yellow cross-band, is found from the Riu Kiu Islands southward. The angel-fish or isabelita (Holacanthus ciliaris), orange-red, sky-blue, and golden, as though gaudily painted, is the best-known species. The vaqueta de dos colores or rock beauty (Holacanthus bicolor), half jet-black, half golden, is scarcely less remarkable. Both are excellent food-fishes of the West Indies. Holacanthus passer is a showy inhabitant of the west coast of Mexico. Holacanthus diacanthus, orange, barred with blue, is one of the gaudiest inhabitants of the coral reefs of Polynesia. Holacanthus flavissimus, golden with some deep-blue markings, and Holacanthus nicobariensis, blackish with white circles, are found with other species in the same waters.

The genus Pomacanthus (Pomacanthodes) includes American species only, still larger in size and differing from Holacanthus in having nine to eleven spines only in the dorsal fin. The young of Pomacanthus are blackish, crossed by many curved yellow cross-bands, which disappear entirely with age. Three species are known, Pomacanthus arcuatus, the black angel, chirivita or portugais, Pomacanthus paru, the Indian-fish or paru of the West Indies, and Pomacanthus zonipectus, "Mojarra de las Piedras," of the west coast of Mexico. All are good food-fishes, but lacking the brilliant colors of Holacanthus and the fine pattern usual in Chætodon.

The Pygæidæ.—Between the Chætodontidæ and the Acanthuridæ we would place the extinct family of Pygæidæ, of the Eocene. In Pygæus gigas and other species the dorsal spines are strong and numerous; there are 5 to 8 species in the anal fin, the scales are shagreen-like, and the teeth seem coarser than in the Chætodontidæ. The tail is apparently unarmed, and the soft dorsal, as in Chætodon, is much shorter than the spinous. To this family the Eocene genera, Aulorhamphus (bolceusis), with produced snout, and Apostasis (croaticus), with long spinous dorsal, probably belong.

The Moorish Idols: Zanclidæ.—The family of Zanclidæ includes a single species, the Moorish idol or kihi kihi, Zanclus canescens. In this family the scales are reduced to a fine shagreen, and in the adult two bony horns grow out over the eye. The dorsal spines are prolonged in filaments and the color is yellow crossed by bars of black. Zanclus canescens is a very handsome fish with the general appearance and habit of a Chætodon, but the form is more exaggerated. It is found throughout Polynesia, from Japan to the off-shore islands of Mexico, and is generally common, though rarely entering rock pools.

Zanclus eocænus is recorded from the Italian Eocene.

The Tangs: Acanthuridæ.—In the next family, Acanthuridæ, the surgeon-fishes or tangs, the scales remain small and shagreen-like, the body is more elongate, the gill-openings still more restricted, and the teeth are flattened and incisor-like. The pubic bone is more elongate, and in all the species some sort of armature is developed on the side of the tail. The spinous dorsal in all is less developed than the soft dorsal. The species abound in the warm seas, especially about the tide pools, and are used as food. They undergo considerable changes with age, the caudal armature being developed by degrees. Nearly all are dull brown in color, but in some a vivid ornamentation is added. Fossil forms are found from the Eocene and later. Most of these are referable to Teuthis and Acanthurus.

The principal genus is Teuthis, characterized by the presence on each side of the tail of a sharp, knife-like, movable spine with the point turned forwards and dropping into a sheath. This spine gives these fishes their name of surgeon-fish, doctor-fish, lancet-fish, tang, barbero, etc., and it forms a very effective weapon against fish or man who would seize one of these creatures by the tail. The species have the center of distribution in the East Indies and have not reached Europe. Three species are found in the West Indies. The blue tang (Teuthis cœruleus) is chiefly bright blue. The common tang, Teuthis chirurgus, is brown with bluish streaks, while a third species, Teuthis bahianus, has a forked caudal fin. Very close to this species is Teuthis crestonis, of the west coast of Mexico, and both are closely related to Teuthis matoides, found from India to Hawaii.

Teuthis triostegus, of Japan and Polynesia and the East Indies, is covered with cross-bands alternately black and pale. In Hawaii this is replaced by the very similar Teuthis sandwichensis. Many species are found about Hawaii and the other Polynesian Islands. Teuthis achilles has a large blotch of brilliant scarlet on the tail, and Teuthis olivaceus a bright-colored mark on the shoulder. Teuthis lineatus, yellow with blue stripes, a showily colored fish of the coral reefs, is often poisonous, its flesh producing ciguatera.

Zebrasoma differs from Teuthis in having but 4 or 5 dorsal spines instead of 10 or 11. In this genus the soft dorsal fin is very high. Zebrasoma flavescens, sometimes brown, sometimes bright yellow, is common in Polynesia; Zebrasoma veliferum, cross-barred with black, is also common.

Ctenochætus (strigosus), unlike the others, is herbivorous and has its teeth loosely implanted in the gums. This species, black with dull orange streaks, was once tabu to the king of Hawaii, who ate it raw, and common people who appropriated it were put to death.

In Xesurus the caudal lancelet is replaced by three or four bony tubercles which have no sharp edge. Xesurus scalprum is common in Japan, and there are three species or more on the west coast of Mexico, Xesurus punctatus and Xesurus laticlavius being most abundant.

In Prionurus (microlepidotus) of the tropical Pacific the armature is still more degraded, about six small plates being developed.

In Acanthurus (Monoceros, Naseus), the unicorn-fish and its relatives, the ventral fins are reduced, having but three soft rays, the caudal spines are very large, blunt, immovable, one placed in front of the other. In most of the species of Acanthurus a long, bony horn grows forward from the cranium above the eye. This is wanting in the young and has various degrees of development in the different species, in some of which it is wholly wanting. The species of Acanthurus reach a large size, and in some the caudal spines are bright scarlet, in others blue. Acanthurus unicornis, the unicorn-fish, is the commonest species and the one with the longest horn. It is abundant in Japan, in Hawaii, and in the East Indies.

Axinurus thynnoides of the East Indies has a long, slim body, with slender tail like a mackerel.

Suborder Amphacanthi, the Siganidæ.—The Amphacanthi (ἄμφϊ, everywhere; ἄκανθα, spine) are spiny-rayed fishes certainly related to the Teuthididæ, but differing from all other fishes in having the last ray of the ventrals spinous as well as the first, the formula being I. 4, I. The anal fin has also six or seven spines; and the maxillary is soldered to the premaxillary. The skeleton is essentially like that of the Acanthuridæ.

The single family, Siganidæ, contains fishes of moderate size, valued as food, and abounding about rocks in shallow water from the Red Sea to Tahiti. The coloration is rather plain olive or brown, sometimes with white spots, sometimes with bluish lines. The species are very much alike and all belong to the single genus Siganus. One species, Siganus fuscescens, dusky with small, pale dots, is a common food-fish of Japan. Others, as Siganus oramin and Siganus vermiculatus, occur in India, and Siganus punctatus, known as lo, abounds about the coral reefs of Samoa. Siganus vulpinus differs from the others in the elongate snout.

A fossil genus, Archoteuthis (glaronensis), is found in the Tertiary of Glarus. It differs from Siganus in the deeper body and in the presence of six instead of seven spines in the anal fin.

The real relationship of the Siganidæ is still uncertain, but the family is probably most nearly allied to the Acanthuridæ, with which the species were first combined by Linnæus, who included both in his genus Teuthis. In the structure of the vertical fins the Siganidæ resemble the extinct genus Pygæus.