The Burgess Animal Book For Children in "A Worker And A Robber"

"Jerry is the very one, the largest member of the Rat family. Sometimes he is spoken of as a little cousin of Paddy the Beaver. Probably this is because he looks something like a small Beaver, builds a house in the water as Paddy does, and lives in very much the same way. The truth is, he is no more closely related to Paddy than he is to the rest of you. He is a true Rat. He is called Muskrat because he carries with him a scent called musk.