=The Leptolepidæ.=—Most primitive of the _Isospondyli_ is the extinct family of _Leptolepidæ_, closely allied to the Ganoid families of _Pholidophoridæ_ and _Oligopleuridæ_. It is composed of graceful, herring-like fishes, with the bones of the head thin but covered with enamel, and the scales thin but firm and enameled on their free portion. There are no fulcra and there is no lateral line. The vertebræ are well developed, but always pierced by the notochord. The genera are _Lycoptera_, _Leptolepis_, _Æthalion_, and _Thrissops_. In _Lycoptera_ of the Jurassic of China the vertebral centra are feebly developed, and the dorsal fin short and posterior. In _Leptolepis_ the anal is short and placed behind the dorsal. There are many species, mostly from the Triassic and lithographic shales of Europe, one being found in the Cretaceous. _Leptolepis coryphænoides_ and _Leptolepis dubius_ are among the more common species. _Æthalion_ (_knorri_) differs in the form of the jaws. In _Thrissops_ the anal fin is long and opposite the dorsal. _Thrissops salmonea_ is found in the lithographic stone; _Thrissops exigua_ in the Cretaceous. In all these early forms there is a hard casque over the brain-cavity, as in the living types, _Amia_ and _Osteoglossum_. [Illustration: FIG. 28.—Ten-pounder, _Elops saurus_ L. An ally of the earliest bony fishes. Virginia. ] [Illustration: FIG. 29.—A primitive Herring-like fish, _Holcolepis lewesiensis_, Mantell, restored. Family _Elopidæ_. English Chalk. (After Woodward.) ] =The Elopidæ.=—The family of _Elopidæ_ contains large fishes herring-like in form and structure, but having a flat membrane-bone or gular plate between the branches of the lower jaw, as in the Ganoid genus _Amia_. The living species are few, abounding in the tropical seas, important for their size and numbers, though not valued as food-fishes save to those who, like the Hawaiians and Japanese, eat fishes raw. These people prefer for that purpose the white-meated or soft-fleshed forms like _Elops_ or _Scarus_ to those which yield a better flavor when cooked. The ten-pounder (_Elops saurus_), pike-like in form but with very weak teeth, is found in tropical America. _Elops machnata_, the jack mariddle, the awaawa of the Hawaiians, abounding in the Pacific, is scarcely if at all different. [Illustration: FIG. 30.—Tarpon or Grande Écaille, _Tarpon atlanticus_ Cuv. & Val. Florida. ] The tarpon, called also grande écaille, silver-king, and sable (_Tarpon atlanticus_), is a favorite game-fish along the coasts of Florida and Carolina. It takes the hook with great spirit, and as it reaches a length of six feet or more it affords much excitement to the successful angler. The very large scales are much used in ornamental work. A similar species of smaller size, also with the last ray of the dorsal very much produced, is _Megalops cyprinoides_ of the East Indies. Other species occur in the South Seas.