Skin covered with scales: body cylindrical, very much elongated: jaws furnished with teeth: no feet.
A third eyelid: body entirely covered with imbricated scales: jaws not dilatable: rudimentary scapular and clavicular bones beneath the skin.
No appearance of extremities visible externally: tympanum concealed beneath the skin: maxillary teeth compressed and hooked; no teeth on the palate.
* This last character, though applicable to the few species met with in this country, must bo received with some limitation in the case of two or three others found on the Continent, in which the collar, though still free at the sides, is interrupted in the middle.
No third eyelid: abdomen covered with broad transverse plates: jaws dilatable: no vestiges of bones of the sternum and shoulder.
- Subcaudal plates arranged in pairs: four nearly equal rows of imperforate teeth above, and two below: no poison-fangs.
Subcaudal plates arranged in pairs: maxillaries armed with poison-fangs, but without ordinary teeth.