• Basilisk: King of the snakes. All other snakes flee before it, because its odor is deadly to them. Kills humans by looking at them. 6 inches long, spotted, severely hydrophobic. “No flying bird may pass unharmed by the basilisk’s face, but however distant it may be it is burnt up and devoured by this animal’s mouth.”
• Sibilus: Similar to the basilisk. Kills by means of hissing.
• Dragon: Largest of the snakes.  Lurks around paths where elephants are accustomed to walk and wraps around their legs. Born in Ethiopia and India “in the fiery intensity of perpetual heat.”
• Amphisbæna:  Has two heads, one on either end of its body.
  
• Prester Asp: Has a mouth that is perpetually open and steaming.
• Dipsas:  So small its bite cannot be felt, but anyone bitten dies of thirst.
• Haemorrhois: “Whoever has  been  bitten  by  it  exudes  blood,  with  the effect that as the veins dissolve it draws out through the blood whatever life there is.”
• Seps: Corrosive. Its venom dissolves bones as well as the rest of the body.
• Cerastes: Uses its 4 horns to lure prey. The most flexible snake.
• Scytale: The pattern of its scales is hypnotic. This is necessary because it moves too slowly to catch unmesmerized prey.
• Chelydros: Amphibious. Makes the earth on which it moves smoke, but can only travel in a straight line “for if it turns when it moves, it immediately makes a sharp noise.”
• Natrix: Deliberately contaminates water by stirring in its poison.
• Cenchris: A snake that cannot bend.
• Parias: A snake that always travels on its tail.
• Jaculus: A flying snake. Launches itself from treetops like a javelin.
  
• Siren: “In Arabia there as snakes with wings, called sirens; they move faster than horses, but they are also said to fly.”
• Salpuga: “The salpuga is a snake that is invisible.”

[All facts from Book XII Section IV of the Etymologies, 2006 Cambridge translation]