FJSH OK O.NTAltlU. 11 



Under this head are now included the Ganoids and the Teleosts. The 

 former group is chiefly composed of extinct forms. While many of its 

 representatives are extremely dissimilar to the bony fishes, there is a 

 gradual series of transitions, and between the Cycloganoidea of the 

 Ganoids and the Clupeoids and others of the true Teleosts, the resemblance 

 is much greater than that between the Cycloganoidea and many other 

 Ganoids. The Ganoids are in fact the most generalized of the true fishes, 

 those nearest the stock from which the Teleosts on the one hand and the 

 Dipnoi, on the other, have sprung. 



Series GANOIDEI. (Ganoid Fishes.) 



The name Ganoidei was first used by Agassiz for those fishes which 

 are armed with bony plates, instead of regular cycloid or ctenoid scales. 

 Later the group has been restricted to those fishes thought to show more 

 or less reptilian or batrachian affinities, and especially affinities with the 

 mailed fishes of the Devonian and Carboniferous ages. The group is a 

 heterogeneous one and one scarcely susceptible of definition. In some of 

 the Ganoids the air bladder still retains its original function, a lung. The 

 existence of the solid optic chiasma, the presence of several valves in the 

 arterial bulb, and of a more or less developed spiral valve in the intestine, 

 distinguish the living Ganoids from all Teleosts. 



Order SELACHOSTOMI. (Paddlefishes.) 



Notochord persistent, the division into vertebrae imperfect Meso- 

 coracoid developed ; no symplectic bone ; premaxillary forming border of 

 mouth; no suboperculum, preoperculum, nor interoperculum ; mesoptery- 

 gium distinct ; basihyals and superior ceratohyal not ossified ; interclavicles 

 present ; maxillaries obsolete ; branchihyals cartilaginous. 



Family POLYODONTID.-i:. (Paddi ekishes.) 



Body fusiform, little compressed, covered with mostly smooth skin. 

 Snout prolonged, expanded into a thin flat blade, the inner portion formed 

 by the produced nasal bones, the outer portion w'ith a reticulate bony 

 framework, the whole somewhat flexible. Mouth broad terminal, but 

 overhung by the spatulate snout, its border formed by the premaxillaries, 

 the maxillaries being obsolete ; jaws with many fine deciduous teeth ; simi- 

 lar teeth on palatines ; no tongue. Spiracles present. Operculum rudi- 

 mentary, its skin produced behind into a long acute flap ; no pseudo- 

 branchiae, or opercular gill ; gills four and one-half ; gill rakers long, in a 

 double series on each arch, the series divided by a broad membrane ; gill 



