The _Chilobranchidæ_ are small sea-fishes from Australia, with the tail longer than the rest of the body, instead of much shorter as in the others. No forms allied to _Symbranchus_ or _Monopterus_ are recorded as fossils. =Order Apodes, or True Eels.=—In this group the shoulder-girdle is free from the skull, and the bones of the jaws are reduced in number, through coalescence of the parts. Three well-marked suborders may be recognized, groups perhaps worthy of still higher rank: _Archencheli_, _Enchelycephali_, and _Colocephali_. =Suborder Archencheli.=—The _Archencheli_, now entirely extinct, are apparently the parents of the eels, having, however, certain traits characteristic of the _Isospondyli_. They retain the separate caudal fin, with the ordinary hypural plate, and Professor Hay has recently found, in an example from the Cretaceous of Mount Lebanon, remains of distinct ventral fins. These traits seem to indicate an almost perfect transition from the _Isospondyli_ to the _Archencheli_. One family may be recognized at present, _Urenchelyidæ_. The earliest known eel, _Urenchelys avus_, occurs in the upper Cretaceous at Mount Lebanon. It represents the family _Urenchelyidæ_, apparently allied to the _Anguillidæ_, but having a separate caudal fin. Its teeth are small, conical, blunt, in many series. There are more than 100 vertebræ, the last expanded in a hypural. Pectorals present. Scales rudimentary; dorsal arising at the occiput. Branchiostegals slender, not curved around the opercle. _Urenchelys anglicus_ is another species, found in the chalk of England. =Suborder Enchelycephali.=—The suborder _Enchelycephali_ (ἔγχελυς, eel; κεφαλή, head) contains the typical eels, in which the shoulder-girdle is free from the skull, the palatopterygoid arch relatively complete, the premaxillaries wanting or rudimentary, the ethmoid and vomer coalesced, forming the front of the upper jaw, the maxillaries lateral, and the cranium with a single condyle. In most of the species pectoral fins are present, and the cranium lacks the combined degradation and specialization shown by the morays (_Colocephali_).