=Gonorhynchidæ.=—To the _Isospondyli_ belongs the small primitive family of _Gonorhynchidæ_, elongate fishes with small mouth, feeble teeth, no air-bladder, small scales of peculiar structure covering the head, weak dentition, the dorsal fin small, and posterior without spines. The mesocoracoid is present as in ordinary _Isospondyli_. _Gonorhynchus abbreviatus_ occurs in Japan, and _Gonorhynchus gonorhynchus_ is found in Australia and about the Cape of Good Hope. Numerous fossil species occur. _Charitosomus lineolatus_ and other species are found in the Cretaceous of Mount Lebanon and elsewhere. Species without teeth from the Oligocene of Europe and America are referred to the genus _Notogoneus_. _Notogoneus osculus_ occurs in the Eocene fresh-water deposits at Green River, Wyoming. It bears a very strong resemblance in form to an ordinary sucker (_Catostomus_), for which reason it was once described by the name of _Protocatostomus_. The living _Gonorhynchidæ_ are all strictly marine. In the small family of _Cromeriidæ_ the head and body are naked. =The Osteoglossidæ.=—Still less closely related to the herring is the family of _Osteoglossidæ_, huge pike-like fishes of the tropical rivers, armed with hard bony scales formed of pieces like mosaic. The largest of all fresh-water fishes is _Arapaima gigas_ of the Amazon region, which reaches a length of fifteen feet and a weight of 400 pounds. It has naturally considerable commercial importance, as have species of _Osteoglossum_, coarse river-fishes which occur in Brazil, Egypt, and the East Indies. _Heterotis nilotica_ is a large fish of the Nile. In some or all of these the air-bladder is cellular or lung-like, like that of a Ganoid. Allied to the _Osteoglossidæ_ is _Phareodus_ (_Dapedoglossus_), a group of large shad-like fossil fishes, with large scales of peculiar mosaic texture and with a bony casque on the head, found in fresh-water deposits of the Green River Eocene. In the perfect specimens of _Phareodus_ (or _Dapedoglossus_) _testis_ the first ray of the pectoral is much enlarged and serrated on its inner edge, a character which may separate these fishes as a family from the true _Osteoglossidæ_. It does not, however, appear in Cope's figures, none of his specimens having the pectorals perfect. In these fishes the teeth are very strong and sharp, the scales are very large and thin, looking like the scales of a parrot-fish, the long dorsal is opposite to the anal and similar to it, and the caudal is truncate. The end of the vertebral column is turned upward.