The _Murænesocidæ_ are large eels remarkable for their strong knife-like teeth. _Murænesox savanna_ occurs in the West Indies and in the Mediterranean, _Murænesox cinereus_ in Japan, and _Murænesox coniceps_ on the west coast of Mexico, all large and fierce, with teeth like shears. The _Myridæ_ are small and worm-like eels closely allied to the congers, having the tail surrounded by a fin, but the nostrils labial. _Myrus myrus_ is found in the Mediterranean. Species of _Eomyrus_, _Rhynchorhinus_, and _Paranguilla_ apparently allied to _Myrus_ occur in the Eocene. Other related families, mostly rare or living in the deep seas, are the _Ilyophidæ_, _Heterocongridæ_, and _Dysommidæ_. [Illustration: FIG. 106.—Larva of Conger-eel (_Leptocephalus conger_), called _Leptocephalus morrissi_. (After Eigenmann.) ] =The Snake-eels.=—Most varied of the families of eels is the _Ophichthyidæ_, snake-like eels recognizable by the form of the tail, which protrudes beyond the fins. Of the many genera found in tropical waters several are remarkable for the sharply defined coloration, suggesting that of the snake. Characteristic species are _Chlevastes colubrinus_ and _Leiuranus semicinctus_, two beautifully banded species of Polynesia, living in the same holes in the reefs and colored in the same fashion. Another is _Callechelys melanotænia_. The commonest species on the Atlantic coast is the plainly colored _Ophichthus gomesi_. [Illustration: FIG 107.—_Xyrias revulsus_ Jordan & Snyder. Family _Ophichthyidæ_. Misaki, Japan. ] In the genus _Sphagebranchus_, very slender eels of the reefs, the fins are almost wanting. [Illustration: FIG. 108.—_Myrichthys pantostigmius_ Jordan & McGregor. Clarion Island. ] [Illustration: FIG. 109.—_Ophichthus ocellatus_ (Le Sueur). Pensacola. ] Allied to the Congers is the small family of duck-billed eels (_Nettastomidæ_) inhabiting moderate depths of the sea. _Nettastoma bolcense_ occurs in the Eocene of Monte Bolca. The produced snout forms a transition to the really extraordinary type of thread-eels or snipe-eels (_Nemichthyidæ_), of which numerous genera and species live in the oceanic depths. In _Nemichthys_ the long, very slender, needle-like jaws are each curved backward so that the mouth cannot by any possibility be shut. The body is excessively slender and the fish swims with swift undulations, often near the surface, and when seen is usually taken for a snake. The best-known species is _Nemichthys scolopaceus_ of the Atlantic and Pacific. _Nemichthys avocetta_, very much like it, has been twice taken in Puget Sound. [Illustration: FIG. 110.—Thread-eel, _Nemichthys avocetta_ Jordan & Gilbert. Vancouver Island. ]