Fig. 193.—Erismatopterus endlicheri Cope. Green River Eocene. (After Cope.)
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.
Fig. 194.—Shoulder-girdle of the Opah, Lampris guttatus (Brünnich), showing the enlarged infraclavicle. (After Boulenger.)
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.