β. Gill-membranes attached to the isthmus.
* Scales well developed; vertebrae 24 or more.
A subocular shelf; mouth small; palate toothless .......... 27. Chaetodontidae.
No subocular shelf; mouth small; palate toothless .......... 28. Drepanidae.
Subocular shelf more or less developed; a superbranchial respiratory organ .......... 31. Osphromenidae.
** Scales minute; mouth small; vertebrae 22 or 23.
Post-temporal not distinctly forked; vertebrae with strong transverse processes; ventrals with 1 spine and 2 to 5 soft rays .......... 29. Acanthuridae.
Post-temporal forked; vertebrae without transverse processes; ventrals with 2 spines and 3 soft rays between them .......... 30. Teuthididae.
b. Lower pharyngeals completely united into one bone, without median suture .......... 32. Embiotocidae.
B. A single nostril on each side; lower pharyngeal bones more or less completely united, but with persistent suture; no subocular shelf; palate toothless .......... 33. Cichlidae.