Symplectic concealed between the quadrate and the hyomandibular .......... 15. Chirocentridae.
Postclavicle on outer side of clavicle; no adipose fin .......... 16. Clupeidae.
Postclavicle on inner side of clavicle; an adipose dorsal fin .......... 17. Salmonidae.
Postclavicle absent; no adipose fin .......... 18. Alepocephalidae.
3. Interoperculum normal; basis cranii simple.
Maxillary large, toothed; praecaudal vertebrae without well-marked parapophyses; scales cycloid or absent; adipose dorsal fin present or absent .......... 19. Stomiatidae.
Mouth small, toothless; vertebrae with strong parapophyses; head and body covered with spiny scales .......... 20. Gonorhynchidae.
Mouth small, toothless; no symplectic; head and body naked .......... 21. Cromeriidae.
† This sign indicates that the group is represented by fossil forms only.
Fam. 1. Pholidophoridae.—Margin of the upper jaw formed by the praemaxillaries and the maxillaries, the latter large and loosely attached; teeth small and conical. Parietal bones separating the supraoccipital from the frontals; opercular bones well developed. Vertebral centra never advanced beyond the annular stage; ribs delicate; no fused or expanded haemal arches at the base of the tail; no epipleurals or epineurals. Fin-fulcra present, but usually small; dorsal and anal fins small, the former above or behind the ventral fins, which are small or may be absent. Scales ganoid, rhombic, those on the flanks united by peg-and-socket joints.