newt
none there is no amphibian starting with n
anything that starts as a tadpole or is slimy... is an amphibian!
salamander
Plains Leopard Frog is an amphibian. It begins with the letter p.
Urocordylus is an extinct amphibian. It begins with the letter u.
bullfrog
Toad.
Kings River Slender Salamander is an amphibian. It begins with the letter k.
salamander
Here's one: Japenese giant salamander
Frog.
There's the American Toad , American Bullfrog and the Alligator Newt .