Suborder Salmopercæ, the Trout-perches: Percopsidæ.—More ancient than the Hemibranchii, and still more distinctly in the line of transition from soft-rayed to spiny-rayed fishes, is the small suborder of Salmopercæ. This is characterized by the presence of the adipose fin of the salmon, in connection with the mouth, scales, and fin-spines of a perch. The premaxillary forms the entire edge of the upper jaw, the maxillary being without teeth. The air-bladder retains a rudimentary duct. The bones of the head are full of mucous cavities, as in the European perch called Gymnocephalus and Acerina. There are two spines in the dorsal and one or two in the anal, while the abdominal ventrals have each a spine and eight rays. Two species only are known among living fishes, these emphasizing more perfectly than any other known forms the close relation really existing between spinous and soft-rayed forms. The single family of Percopsidæ would seem to find its place in Cretaceous rocks rather than in the waters of to-day.

Percopsis guttata, the trout-perch or sand-roller of the Great Lakes, is a pale translucent fish with dark spots, reaching a length of six inches. It abounds in the Great Lakes and their tributaries and is occasionally found in the Delaware, Ohio, Kansas, and other rivers and northwestward as far as Medicine Hat on the Saskatchewan. It is easily taken with a hook from the piers at Chicago.

Columbia transmontana is another little fish of similar type, but rougher and more distinctly perch-like. It is found in sandy or weedy lagoons throughout the lower basin of the Columbia, where it was first noticed by Dr. Eigenmann in 1892. From the point of view of structure and classification, this left-over form is one of the most remarkable of American fishes.

Erismatopteridæ.—Here should perhaps be placed the family of Erismatopteridæ, represented by Erismatopterus levatus and other species of the Green River Eocene shales. In Erismatopterus the short dorsal has two or three spines, there are two or three spines in the anal, and the abdominal ventrals are opposite the dorsal. Allied to Erismatopterus is Amphiplaga of the same deposits.

We cannot, however, feel sure that these extinct fragments, however well preserved, belonged to fishes having an adipose fin. Among spiny-rayed fishes the Percopsidæ alone retain this character, and the real affinities of Erismatopterus may be with Aphredoderidæ and other percoid forms.

The relations of the extinct family of Asineopidæ are also still uncertain. This group comprises fresh-water fishes said to be allied to the Aphredoderidæ, but with the pelvic bones not forked. Asineops pauciradiata, squamifrons and viridensis are described from the Green River shales. With Erismatopterus all these fishes may belong to the suborder of Salmopercæ, but, as above stated, the possession of the adipose fin, the most characteristic trait of the Salmopercæ, cannot be verified in the fossil remains.

Suborder Selenichthyes, the Opahs: Lamprididæ.—We may bring together as constituting another suborder certain forms of uncertain relationship, but which seem to be transitional between deep-bodied extinct Ganoids and the forms allied to Platax, Zeus, and Antigonia. The name of Selenichthyes (σηλήνη, moon; ἰχθύς, fish) is suggested by Boulenger for the group of opahs, or moonfishes. These are characterized by the highly compressed body, the great development of a large hypocoracoid, and especially by the structure of the ventral fins, which are composed of about fifteen rays instead of the one spine and five rays characteristic of the specialized perch-like fishes. The living forms of this type are further characterized by the partial or total absence of the spinous dorsal, by the small oblique mouth, and the prominence of the ventral curve of the body. A thorough study of the osteology of these forms living and fossil will be necessary before the group can be properly defined. The large bone above mentioned was at first considered by Boulenger as the interclavicle or infraclavicle, the hypocoracoid being regarded by him as displaced, lying with the actinosts. But it is certain, from the studies of Mr. Starks, that this bone is the real hypocoracoid, which in this case is simply exaggerated in size, but placed as in ordinary fishes.

The single living family, Lamprididæ, contains but one species, Lampris guttatus, known as opah, moonfish, mariposa, cravo, Jerusalem haddock, or San Pedro fish. This species reaches a length of six feet and a weight of 500 to 600 pounds. Fig. 199 (Vol. I) is taken from a photograph of an example weighing 317½ pounds taken near Honolulu by Mr. E. L. Berndt. The body is almost as deep as long, plump and smooth, without scales or bony plates. The vertebræ are forty-five in number, and the large ventrals contain about fifteen rays. The dorsal is without spines, the small mouth without teeth. The color is a "rich brocade of silver and lilac, rosy on the belly, everywhere with round silvery spots." The head and back have ultramarine tints, the jaws and fins are vermilion. On a drawing of this fish made at Sable Island in 1856, Mr. James Farquhar wrote (to Dr. J. Bernard Gilpin): "Just imagine the body, a beautiful silver interspersed with spots of a lighter color about the size of sixpence, the eyes very large and brilliant, with a golden ring around them. You will then have some idea of the splendid appearance of the fish when fresh. If Caligula had seen them I might have realized a fortune."

The skeleton of the opah is very firm and heavy. The flesh is of varying shades of salmon-red, tender, oily, and of a rich, exquisite flavor scarcely surpassed by any other fish whatsoever.

The opah is a rare fish, swimming slowly near the surface and ranging very widely in all the warm seas. It was first noticed in Norway by Gunner, the good bishop of Throndhjem, about 1780. It was soon after recorded from Elsinore, Torbay, and Madeira, and is occasionally taken in various places in Europe. It is also recorded from Newfoundland, Sable Island, Cuba, Monterey, San Pedro Point (near San Francisco), Santa Catalina, Honolulu, and Japan.

The specimen studied by the writer came ashore at Monterey in an injured condition, having been worsted in a struggle with some better-armed fish.

Allied to Lampris is the imposing extinct species known as Semiophorus velifer from the Eocene of Monte Bolca near Verona, the type of the extinct family of Semiophoridæ. This is a deep compressed fish, with very high spinous dorsal and very long, many-rayed ventrals. Other related species are known also from the Eocene. There is no evidence of any close relation between these fishes with Caranx or Platax, with which Woodward associates Semiophorus.

The Semiophoridæ differ from the Lamprididæ chiefly in the development of the spinous dorsal fin, which is composed of many slender rays.

Suborder Zeoidea.—Not far from the Selenichthyes and the Berycoidei we may place the singular group of John Dories, or zeoid fishes. These have the ventral fins thoracic and many-rayed, the dorsal fin provided with spines, and the post-temporal, as in the Chætodontidæ, fused with the skull. Dr. Boulenger calls attention to the close relation of these fishes to the flounders, and suggests the possible derivation of both from a synthetic type, the Amphistiidæ, found in the European Eocene. The Amphistiidæ, Zeidæ, and flounders are united by him to form the group or suborder Zeorhombi, characterized by the thoracic ventrals, which have the rays not I, 5 in number, by the progressive degeneration of the fin-spines and the progressive twisting of the cranium, bringing the two eyes to the same side of the head. It is not certain that the flounders are really derived from Zeus-like fishes, but no other guess as to their origin has more elements of probability.

We may, however, regard the Zeoidea on the one hand and the Heterosomata on the other as distinct suborders. This is certain, that the flounders are descended from spiny-rayed forms and that they have no affinities with the codfishes.

Amphistiidæ.—The Amphistiidæ, now extinct, are deep-bodied, compressed fishes, with long, continuous dorsal and anal fins in which a few of the anterior rays are simple, slender spines scarcely differentiated from the soft rays. The form of body and the structure of the fins are essentially as in the flounders, from which they differ chiefly by the symmetry of the head, the eyes being normally placed. Amphistium paradoxum is described by Agassiz from the upper Eocene. It occurs in Italy and France. In its dorsal and anal fins there are about twenty-two rays, the first three or four undivided. The teeth are minute or absent and there is a high supraoccipital crest.

The John Dories: Zeidæ.—The singular family of Zeidæ, or John Dories, agrees with Chætodonts in the single character of the fusion of the post-temporal with the skull. The species, however, diverge widely in other regards, and their ventral fins are essentially those of the Berycoids. In all the species there are seven to nine soft rays in the ventral fins, as in the Berycoid fishes. Probably the character of the fused post-temporal has been independently derived. The anterior vertebræ in Zeus, as in Chætodon, are closely crowded together. In the Zeidæ the spinous dorsal is well developed, the body naked or with very thin scales, and provided with bony warts at least around the bases of dorsal and anal fins. The species are mostly of small size, silvery in color, living in moderate depths in warm seas. The best-known genus is Zeus, which is a group of shore-fishes of the waters of Asia and Europe. The common John Dory (called in Germany Härings-König, or king of the herrings), Zeus faber, abounds in shallow bays on the coasts of Europe. It reaches a length of nearly a foot, and is a striking feature of the markets of southern Europe. The dorsal spines are high, the mouth large, and on the sides is a black ring, said by some to be the mark of the thumb of St. Peter, who is reported to have taken a coin from the mouth of this species. A black spot on several other species is associated with the same legend.

On the coasts of Japan abounds the Matao, or target-fish (Zeus japonicus), very similar to the European species and like it in form and color. Zenopsis nebulosa and Zen itea also occur on the coasts of Japan. The remaining Zeidæ (Cyttus, Zenopsis, Zenion, etc.) are all rare species occasionally dredged especially in the Australian region. Zeus priscus is recorded from the Tertiary, and Cyttoides glaronensis from the upper Eocene of Glavus.

Grammicolepidæ.—The Grammicolepidæ, represented by a single species, Grammicolepis brachiusculus, rarely taken off the coast of Cuba, is related to the Zeidæ. It has rough, ridged, parchment-like scales deeper than long. The ventrals are thoracic, with the rays in increased number, as in Zeus and Beryx, with each of which it suggests affinity.