In "The Monkey's Paw" by W.W. Jacobs, how would you describe the appearance of the monkey's paw?

The monkey’s paw is a disembodied mummified monkey’s paw.
The monkey’s paw is a talisman that supposedly had a spell put on it by a fakir in India.  You can wish on it, and your wish will come true.  It just won’t come true in the way you intended.  Sergeant-major Morris, who brings the Whites the paw, explains that the person who last had the paw wished for death after using it.
The sergeant-major describes the paw as ordinary.

"To look at," said the sergeant-major, fumbling in his pocket, "it's just an ordinary little paw, dried to a mummy."

Basically, someone cut the paw off a monkey, and over time it has been mummified.  The Whites seem to find its appearance disturbing even though Morris describes it as ordinary.  However, due to the spell it now has magical powers.
The monkey’s paw may make the Whites feel disturbed because of the way Morris describes its powers, rather than how it looks.  He makes it seem scary.  Let’s face it, parts of monkeys are a little gross anyway.
After throwing the monkey's paw into the fire, Morris warned the Whites to leave it alone.  They were curious though.  They ended up making a wish, as a lark.

Mr. White took the paw from his pocket and eyed it dubiously. "I don't know what to wish for, and that's a fact," he said slowly. "It seems to me I've got all I want."
  "If you only cleared the house, you'd be quite happy, wouldn't you?" said Herbert, with his hand on his shoulder. "Well, wish for two hundred pounds, then; that'll just do it."

They would later regret making this wish, because the Whites found out why the last person wished for death.  The Whites got their first wish in the worst way, when they got the money but their son was killed.  Then, Mrs. White wished him back to life.  Her husband used the last wish to reverse that wish.