The mouth is usually more or less protractile and always toothless; the lower pharyngeal bones, which are large and falciform, subparallel to the branchial arches, are provided with teeth, often large and highly specialized, in one, two or three series (pharyngeal teeth), usually working against a horny plate attached to a vertical process of the basioccipital bone produced under the anterior vertebrae, mastication being performed in the gullet.
- Acrodont; tongue broad and thick, not protractile; no osteoderms. Old World.
- Pleurodont; tongue broad and thick, not protractile; no osteoderms. America, Madagascar and Fiji Islands.
- Pleurodont; tongue short, villose, scarcely protractile, feebly nicked at the tip. With osteoderms at least upon the skull, where they roof in the temporal region.