These were eliminated by Johannes Muller, who recognized the archaic characters common to the existing forms. Still later Huxley re moved the crossopterygians, and others have shown that the Ostracophori and Arthrodira should be placed far from the garpike in sys tematic classification. Cope and Woodward have dropped the name ganoid altogether as pro, ductive of confusion through the many mean. Wigs attached to it. Others have used it as a handy group name for the orders of archaic Actinopteri. • For these varied and more or .less divergent groups it seems convenient to retain it.
The order (nog., a loosing; fin) comprises the earliest ganoids, be ginning in the Devonian which have the body covered with enameled scales. The families are Palcroniscidee, Platysomider, Dietyopygider and Dorypternie. The order Chondrostei Czovdpos, cartilage; bartov, bone, includes a great variety of forms, characterized by the less cartilaginous skeleton, .the distinctly heterocercal tail, and the- presence of bony plates, rather than scales, on most parts of the body. These represent a degenerate offshoot from the Lysopteri, the form being less like that of the typical fishes. The earliest members of this group appear in the Tertiary, the most primi tive family being the Chondrosteidee (extinct).
Amia calva (Amiatus ealvus), in the waters of the eastern United States. In these forms there is a gradual transition from diamond-shaped scales, covered with enamel, to the cycloid scales of the ordinary soft-rayed fishes. The line separating the Lepidostei and Halecotnorphi from each other and 'from the Isospondyli is a very narrow one.
Sub-class Teleostei or Bony Fishes.— The fishes which still remain for discussion con stitute the great sub-class or series of Teleostei or bony fishes. They lack wholly or partly the ganoid traits, or show them only in the em bryo. The tail is slightly if at all heterocercal. the fulcra disappear, the actinosts of the pec toral fins are feW and large, rarely if ever over five in number, the air-bladder is no longer cellular in most species, nor does it assist in respiration. The optic nerves are separate, one running to each eye without •chiasma. The skeleton is almost entirely bony, the notochord usually disappearing entirely with age. The valves in the arterial bulb are reduced in. num ber, and the spiral valve of the intestines dis Another family is that of Belonorhynchidte (extinct). The (sturgeons) are well represented among living fishes. The order
Selachostomi (anaxoc, shark; araya, mouth) includes the paddle-fishes two living species, and one extinct, in the Eocene. The order Pycnodonti including the family of Pycnadontide (extinct), consists of a deep bodied, compressed fishes with small mouths and a peculiar physiognomy. The order Lepi dastei (yen's, scale; Oariov, bone) includes numerous families with rhombic enameled scales. The, families are Semionotidce, Leh dotidce, Isopholidte, Macrosemitcle, Pholidop. hornier, Aspidorhynchide, and LePieosteidee, all extinct save the 1,episosteide, represented by four species known as garpike in the rivers of North America. The earliest fossil garpikes occur in the Eocene. The Hakcomorphi (halec, herring; 70P(14. form) comprise the Pocky cornsida Protosphyrernicke, Liodesmidce, Dli gopleuride, and Amiide. All these have perished, except the •Amiicke, which group is represented by a single species, the Bowfin, appears. Traces of each of the ganoid traits may persist somewhere in some group, but as a whole we see a distinct specialization and a distinct movement toward the fish type with the loss of characters distinctive of sharks, dipnoi, and ganoids. In a general way the skeleton of all teleosts corresponds with that of the striped bass, and the visceral anatomy is in all cases sufficiently like that of the sunfish.
The mesocoracoid or prwcoracoid arch, found in all ganoids, persists in the less special-. ized types of bony fishes, although no trace of it is found in the perch-like forms. With all this there is found among the bony fishes, an infinite variety in details of structure. For this reason the Teleostei must be broken into many orders and these orders are very different in value and in degrees of distinctness, the various groups being joined by numerous and puzzling intergradations.
Order Of the various subor dinate groups of bony fishes there can be no question as to which is most primitive in struc ture or as to which stands nearest the orders of ganoids. Earliest of the bony fishes in geological time is the order of Isospondyli (loos equal; vertebra), containing the allies recent and fossil of the herring and the trout. This order contains those soft-rayed fishes which have the ventral fins abdominal, the mesocoracoid or pracoracoid arch developed (sometimes lost in degeneration), and the an terior vertebra unmodified, essentially similar to the others.